Esc alternates between the last two panes; Toggleterm is gone

Esc ran Toggleterm, which hopped between the newest DOC and the newest
TERMINAL. That distinction never earned its keep. It made Esc unpredictable —
which of three panes you landed on depended on their kinds, not on where you
had been — and it could not alternate between two files at all, which is the
case you hit most. Editing two files, Esc did nothing.

The replacement already existed. Last (SPC j j) is "the pane you were in
before this one, whichever it was": it walks the jump stack for the newest
entry naming a different pane and restores its line and column. So Esc, and
Shift-Esc in tty, now run Last, and Toggleterm is deleted rather than renamed
— a third implementation of "go to the other pane" was the thing to avoid.
SPC w t goes with it; the w group is the four directional moves, and the jump
group already had SPC j j.

Held down, Esc alternates. Two files, a file and its shell, a file and a
+Search — all the same, because Last has no notion of kind to get wrong.

This depends on the swap in the same series: Last reads the stack backwards,
and until hopping stopped appending, the pane you came from could fall off it.

windownav.snap needed only its keys and prose changed — its golden did not
move at all, which is the useful evidence here: for the one scenario the old
builtin handled well, Last produces an identical focus sequence.

Coverage for what it did not handle is new: a unit test opens a second FILE by
looking its name and asserts Esc alternates between two panes of the SAME
kind, which is the case that used to be a no-op.

Docs follow: tutor.txt, docs/helix-keys.md, docs/design.typ, and the builtin
index goldens, which are now one row shorter.

75/75 snapshots, both unit suites, and the macOS ABI build all pass.

1 files changed, 6 insertions, 6 deletions

diff --git a/test/snapshots/lookpanes.golden b/test/snapshots/lookpanes.golden
index 276de16b..acdb02a3 100644
--- a/test/snapshots/lookpanes.golden
+++ b/test/snapshots/lookpanes.golden
@@ -1,6 +1,6 @@
 == snap shells grid=130x50 cursor=122,3
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd New Del
+|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd      New Del
 |     1 both.txt
 |     2 b-marker                                                    alpha  beta  zzboot.txt    zqonly.txt pick.txt twin.txt
 |
@@ -51,7 +51,7 @@
 |
 == snap other-dir grid=130x50 cursor=7,27
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd New Del
+|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd      New Del
 |     1 both.txt
 |     2 b-marker                                                    alpha  beta  zzboot.txt    zqonly.txt pick.txt twin.txt
 |
@@ -102,7 +102,7 @@
 |
 == snap clicked-wins grid=130x50 cursor=7,15
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd New Del
+|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd      New Del
 |     1 both.txt
 |     2 b-marker                                                    alpha  beta  zzboot.txt    zqonly.txt pick.txt twin.txt
 |
@@ -153,7 +153,7 @@
 |
 == snap mru-alpha grid=130x50 cursor=7,21
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd New Del
+|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd      New Del
 |     1 both.txt
 |     2 b-marker                                                    alpha  beta  zzboot.txt    zqonly.txt pick.txt twin.txt
 |
@@ -204,7 +204,7 @@
 |
 == snap mru-beta grid=130x50 cursor=7,9
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd New Del
+|  /tmp/pardes-snap/lookpanes/cwd/beta/bmark.txt Save New Del       /tmp/pardes-snap/lookpanes/cwd      New Del
 |     1 both.txt
 |     2 b-marker                                                    alpha  beta  zzboot.txt    zqonly.txt pick.txt twin.txt
 |
@@ -255,7 +255,7 @@
 |
 == style mru-beta
 |0: 0-56 #949494,#121212, 57-129 d,#121212,
-|1: 0-1 #ffffff,#262626, 2-59 #949494,#121212, 60-64 d,#121212, 65-66 #ffffff,#262626, 67-104 #949494,#121212, 105-129 d,#121212,
+|1: 0-1 #ffffff,#262626, 2-59 #949494,#121212, 60-64 d,#121212, 65-66 #ffffff,#262626, 67-109 #949494,#121212, 110-129 d,#121212,
 |2: 0-0 d,#444444, 1-1 d,#080808, 2-6 #626262,#080808, 7-14 #bdbdbd,#080808, 15-64 d,#080808, 65-65 d,#444444, 66-66 d,#080808, 67-129 #bdbdbd,#080808,
 |3: 0-0 d,#444444, 1-1 d,#080808, 2-6 #626262,#080808, 7-14 #bdbdbd,#080808, 15-64 d,#080808, 65-65 d,#444444, 66-66 d,#080808, 67-121 #bdbdbd,#080808, 122-129 d,#080808,
 |4: 0-0 d,#444444, 1-1 d,#080808, 2-6 #626262,#080808, 7-64 d,#080808, 65-65 d,#444444, 66-66 d,#080808, 67-129 #bdbdbd,#080808,