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, 14 insertions, 14 deletions

diff --git a/test/snapshots/lsp.golden b/test/snapshots/lsp.golden
index 46d4a94a..48577a7f 100644
--- a/test/snapshots/lsp.golden
+++ b/test/snapshots/lsp.golden
@@ -1,6 +1,6 @@
 == snap opened grid=120x40 cursor=7,2
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -41,7 +41,7 @@
 |
 == snap cursor grid=120x40 cursor=17,9
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -82,7 +82,7 @@
 |
 == snap definition grid=120x40 cursor=15,4
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -123,7 +123,7 @@
 |
 == snap hover grid=120x40 cursor=15,4
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -159,12 +159,12 @@
 |
 |
 |
-|  /tmp/pardes-snap/lsp/cwd/+Hover New Del
+|  /tmp/pardes-snap/lsp/cwd/+Hover                                                            New Del
 |     1 fn helper(x: u32) u32
 |     2 (fn (u32) u32)
 == snap symbols grid=120x40 cursor=15,4
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -196,16 +196,16 @@
 |
 |
 |
-|  /tmp/pardes-snap/lsp/cwd/+Search New Del
+|  /tmp/pardes-snap/lsp/cwd/+Search                                                           New Del
 |     1 /tmp/pardes-snap/lsp/cwd/a.zig:1:7-9 std
 |     2 /tmp/pardes-snap/lsp/cwd/a.zig:3:4-9 helper  fn helper(x: u32) u32
 |     3 /tmp/pardes-snap/lsp/cwd/a.zig:7:8-11 main  fn main() void
-|  /tmp/pardes-snap/lsp/cwd/+Hover New Del
+|  /tmp/pardes-snap/lsp/cwd/+Hover                                                            New Del
 |     1 fn helper(x: u32) u32
 |     2 (fn (u32) u32)
 == snap step grid=120x40 cursor=15,2
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -237,16 +237,16 @@
 |
 |
 |
-|  /tmp/pardes-snap/lsp/cwd/+Search New Del
+|  /tmp/pardes-snap/lsp/cwd/+Search                                                           New Del
 |     1 /tmp/pardes-snap/lsp/cwd/a.zig:1:7-9 std
 |     2 /tmp/pardes-snap/lsp/cwd/a.zig:3:4-9 helper  fn helper(x: u32) u32
 |     3 /tmp/pardes-snap/lsp/cwd/a.zig:7:8-11 main  fn main() void
-|  /tmp/pardes-snap/lsp/cwd/+Hover New Del
+|  /tmp/pardes-snap/lsp/cwd/+Hover                                                            New Del
 |     1 fn helper(x: u32) u32
 |     2 (fn (u32) u32)
 == snap nothing grid=120x40 cursor=7,4
 |New Newcol Find Grep Help Tutor Dump NextColor Debug Kill
-|  /tmp/pardes-snap/lsp/cwd/a.zig Save New Del
+|  /tmp/pardes-snap/lsp/cwd/a.zig                                                        Save New Del
 |     1 const std = @import("std");
 |     2
 |     3 fn helper(x: u32) u32 {
@@ -278,10 +278,10 @@
 |
 |
 |
-|  /tmp/pardes-snap/lsp/cwd/+Search New Del
+|  /tmp/pardes-snap/lsp/cwd/+Search                                                           New Del
 |     1 /tmp/pardes-snap/lsp/cwd/a.zig:1:7-9 std
 |     2 /tmp/pardes-snap/lsp/cwd/a.zig:3:4-9 helper  fn helper(x: u32) u32
 |     3 /tmp/pardes-snap/lsp/cwd/a.zig:7:8-11 main  fn main() void
-|  /tmp/pardes-snap/lsp/cwd/+Hover New Del
+|  /tmp/pardes-snap/lsp/cwd/+Hover                                                            New Del
 |     1 fn helper(x: u32) u32
 |     2 (fn (u32) u32)