Help lists every builtin and every way to reach it

Not a second builtin: Help already rendered "every builtin with a leader path
and the key that runs it", and the ask is "every builtin and every shortcut" —
the same listing with three more rows and one more column. A new builtin would
have been a second renderer over a superset of the same rows, and the two would
drift the first time a column moved. The prefix filter is now the degenerate
case of the index rather than a separate mode: SPC h ? reads the same array
with prefix "h", and the path-less builtins fall out on their own because an
empty path starts with nothing.

The shortcut column is folded, never typed: chordName spells a chord from Key's
OWN declarations, so a new special key names itself and an unnamed
non-printable codepoint is a compile error instead of garbage; shortcuts()
walks the cmd columns of window_keys and jump_keys, look_cmd/exec_cmd with
their keys and buttons, and topbar_str. Retarget a binding in config.zig and
this re-renders.

So Look reads `enter, right-click`, Back reads `C-o`, Kill reads `topbar`, and
Theme reads nothing at all — which is the information.

Not a picker, deliberately: n/N stepping a list holding Kill, Del and Delcol
would end the session. The names are live text, so middle-click the one you
want.

Alt-n, Alt-c, the tty toggle and the cut/paste chords cannot appear — they are
inline handlers that reach no builtin, so there is no row to put them on. Make
one a struct with a cmd column beside its binding and it appears for free.

Three goldens moved, all of them the +Help buffer's contents.

1 files changed, 366 insertions, 0 deletions

diff --git a/test/snapshots/builtins.golden b/test/snapshots/builtins.golden
new file mode 100644
index 00000000..40152d5b
--- /dev/null
+++ b/test/snapshots/builtins.golden
@@ -0,0 +1,366 @@
+== snap boot grid=120x60 cursor=7,2
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/builtins/cwd/notes.txt Save Del        NOR /tmp/pardes-snap/builtins/cwd Del
+|     1 line 1
+|     2 line 2                                                 notes.txt
+|     3 line 3
+|     4 line 4
+|     5 line 5
+|     6 line 6
+|     7
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+== snap index grid=120x60 cursor=7,32
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/builtins/cwd/notes.txt Save Del        NOR /tmp/pardes-snap/builtins/cwd Del
+|     1 line 1
+|     2 line 2                                                 notes.txt
+|     3 line 3
+|     4 line 4
+|     5 line 5
+|     6 line 6
+|     7
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|  NOR /tmp/pardes-snap/builtins/cwd/+Help Del
+|     1 pardes builtins, and how to run each:
+|     2 SPC and its keys, a chord, a button, the
+|     3 topbar - or the name, executed anywhere.
+|     4
+|     5 SPC ?     Help            topbar
+|     6 SPC c d   Delcol
+|     7 SPC c n   Newcol          topbar
+|     8 SPC d     Del
+|     9 SPC f f   Find            topbar
+|    10 SPC f g   Grep            topbar
+|    11 SPC f s   Save
+|    12 SPC h t   Tutor           topbar
+|    13 SPC j i   Forward         C-i
+|    14 SPC j j   Last
+|    15 SPC j l   Jumplist
+|    16 SPC j o   Back            C-o
+|    17 SPC k     Kill            topbar
+|    18 SPC l D   WsDiagnostics
+|    19 SPC l S   WsSymbols
+|    20 SPC l a   CodeAction
+|    21 SPC l d   Diagnostics
+|    22 SPC l h   SelectRefs
+|    23 SPC l i   Lspinfo
+|    24 SPC l k   Hover
+|    25 SPC l r   Rename
+|    26 SPC l s   Symbols
+|    27 SPC l w   Lspwhy
+|    28 SPC s d   Dump            topbar
+== snap index-tail grid=120x60 cursor=7,58
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/builtins/cwd/notes.txt Save Del        NOR /tmp/pardes-snap/builtins/cwd Del
+|     1 line 1
+|     2 line 2                                                 notes.txt
+|     3 line 3
+|     4 line 4
+|     5 line 5
+|     6 line 6
+|     7
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|  NOR /tmp/pardes-snap/builtins/cwd/+Help Del
+|    19 SPC l S   WsSymbols
+|    20 SPC l a   CodeAction
+|    21 SPC l d   Diagnostics
+|    22 SPC l h   SelectRefs
+|    23 SPC l i   Lspinfo
+|    24 SPC l k   Hover
+|    25 SPC l r   Rename
+|    26 SPC l s   Symbols
+|    27 SPC l w   Lspwhy
+|    28 SPC s d   Dump            topbar
+|    29 SPC s r   Restore
+|    30 SPC t a   Ascii
+|    31 SPC t c   Colors
+|    32 SPC t d   Debug           topbar
+|    33 SPC t l   Palette
+|    34 SPC t n   NextColor       topbar
+|    35 SPC t p   Petscii
+|    36 SPC t r   Crt
+|    37 SPC t t   ThemeSel
+|    38 SPC w h   Left            C-w h, C-w left
+|    39 SPC w j   Down            C-w j, C-w down
+|    40 SPC w k   Up              C-w k, C-w up
+|    41 SPC w l   Right           C-w l, C-w right
+|    42 SPC w t   Toggleterm
+|    43           Look            enter, right-click
+|    44           Exec            tab, middle-click
+|    45           Theme
+|    46
+== snap not-a-picker grid=120x60 cursor=7,58
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/builtins/cwd/notes.txt Save Del        NOR /tmp/pardes-snap/builtins/cwd Del
+|     1 line 1
+|     2 line 2                                                 notes.txt
+|     3 line 3
+|     4 line 4
+|     5 line 5
+|     6 line 6
+|     7
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|  NOR /tmp/pardes-snap/builtins/cwd/+Help Del
+|    19 SPC l S   WsSymbols
+|    20 SPC l a   CodeAction
+|    21 SPC l d   Diagnostics
+|    22 SPC l h   SelectRefs
+|    23 SPC l i   Lspinfo
+|    24 SPC l k   Hover
+|    25 SPC l r   Rename
+|    26 SPC l s   Symbols
+|    27 SPC l w   Lspwhy
+|    28 SPC s d   Dump            topbar
+|    29 SPC s r   Restore
+|    30 SPC t a   Ascii
+|    31 SPC t c   Colors
+|    32 SPC t d   Debug           topbar
+|    33 SPC t l   Palette
+|    34 SPC t n   NextColor       topbar
+|    35 SPC t p   Petscii
+|    36 SPC t r   Crt
+|    37 SPC t t   ThemeSel
+|    38 SPC w h   Left            C-w h, C-w left
+|    39 SPC w j   Down            C-w j, C-w down
+|    40 SPC w k   Up              C-w k, C-w up
+|    41 SPC w l   Right           C-w l, C-w right
+|    42 SPC w t   Toggleterm
+|    43           Look            enter, right-click
+|    44           Exec            tab, middle-click
+|    45           Theme
+|    46
+== snap window-group grid=120x60 cursor=7,32
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/builtins/cwd/notes.txt Save Del        NOR /tmp/pardes-snap/builtins/cwd Del
+|     1 line 1
+|     2 line 2                                                 notes.txt
+|     3 line 3
+|     4 line 4
+|     5 line 5
+|     6 line 6
+|     7
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|  NOR /tmp/pardes-snap/builtins/cwd/+Help Del
+|     1 pardes builtins under SPC w
+|     2
+|     3 SPC w h   Left            C-w h, C-w left
+|     4 SPC w j   Down            C-w j, C-w down
+|     5 SPC w k   Up              C-w k, C-w up
+|     6 SPC w l   Right           C-w l, C-w right
+|     7 SPC w t   Toggleterm
+|     8
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+|
+== snap tutor-from-index grid=120x60 cursor=7,17
+|Kill Newcol Tutor Debug NextColor Dump Find Grep Help
+|  NOR /tmp/pardes-snap/builtins/cwd/notes.txt Save Del        NOR /tmp/pardes-snap/builtins/cwd Del
+|     1 line 1
+|     2 line 2                                                 notes.txt
+|     3 line 3
+|     4 line 4
+|     5 line 5
+|     6 line 6
+|     7
+|
+|
+|
+|
+|
+|
+|
+|  NOR /Tutor Save Del
+|     1
+|     2                                PARDES TUTOR
+|     3                      tmux + vi + acme, from scratch.
+|     4
+|     5         The model is acme's: EVERYTHING is text, edit
+|     6         the same way. Modal editing (helix-style) liv
+|     7         Press j until you reach the introduction.
+|     8
+|     9
+|    10 =====================================================
+|    11 =                      INTRODUCTION
+|    12 =====================================================
+|    13
+|    14  Pardes is tmux + vi + acme, made from scratch. The f
+|  NOR /tmp/pardes-snap/builtins/cwd/+Help Del
+|     1 pardes builtins, and how to run each:
+|     2 SPC and its keys, a chord, a button, the
+|     3 topbar - or the name, executed anywhere.
+|     4
+|     5 SPC ?     Help            topbar
+|     6 SPC c d   Delcol
+|     7 SPC c n   Newcol          topbar
+|     8 SPC d     Del
+|     9 SPC f f   Find            topbar
+|    10 SPC f g   Grep            topbar
+|    11 SPC f s   Save
+|    12 SPC h t   Tutor           topbar
+|    13 SPC j i   Forward         C-i
+|    14 SPC j j   Last
+|    15 SPC j l   Jumplist
+|    16 SPC j o   Back            C-o
+|    17 SPC k     Kill            topbar
+|    18 SPC l D   WsDiagnostics
+|    19 SPC l S   WsSymbols
+|    20 SPC l a   CodeAction
+|    21 SPC l d   Diagnostics
+|    22 SPC l h   SelectRefs
+|    23 SPC l i   Lspinfo
+|    24 SPC l k   Hover
+|    25 SPC l r   Rename
+|    26 SPC l s   Symbols
+|    27 SPC l w   Lspwhy
+|    28 SPC s d   Dump            topbar