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, 8 insertions, 8 deletions

diff --git a/test/snapshots/tagnav.golden b/test/snapshots/tagnav.golden
index 72cfd175..e3e5e8d2 100644
--- a/test/snapshots/tagnav.golden
+++ b/test/snapshots/tagnav.golden
@@ -29,7 +29,7 @@
 |
 |
 |
-== snap colon grid=100x30 cursor=35,1
+== snap colon grid=100x30 cursor=36,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -60,7 +60,7 @@
 |
 |
 |
-== snap right-tag grid=100x30 cursor=79,1
+== snap right-tag grid=100x30 cursor=80,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -91,7 +91,7 @@
 |
 |
 |
-== snap left-tag grid=100x30 cursor=35,1
+== snap left-tag grid=100x30 cursor=36,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -122,7 +122,7 @@
 |
 |
 |
-== snap down-tag grid=100x30 cursor=29,16
+== snap down-tag grid=100x30 cursor=30,16
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -153,7 +153,7 @@
 |
 |
 |
-== snap up-tag grid=100x30 cursor=35,1
+== snap up-tag grid=100x30 cursor=36,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -277,7 +277,7 @@
 |
 |
 |
-== snap back-down grid=100x30 cursor=35,1
+== snap back-down grid=100x30 cursor=36,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -308,7 +308,7 @@
 |
 |
 |
-== snap arrows-still-motion grid=100x30 cursor=37,1
+== snap arrows-still-motion grid=100x30 cursor=38,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del    /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha
@@ -401,7 +401,7 @@
 |
 |
 |
-== snap tty-tag grid=100x30 cursor=79,1
+== snap tty-tag grid=100x30 cursor=80,1
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
 |  /tmp/pardes-snap/tagnav/cwd/w.txt Save New Del  $ /tmp/pardes-snap/tagnav/cwd New Del
 |     1 alpha