themes: one file each, generated from helix and zed, picked by stepping a list

Each theme is a .zig file of pure data and nothing enumerates them by hand —
fold() walks the container's declarations, so a theme is a file and that is the
whole registration. Field by field rather than a wholesale coercion, which
makes a missing field a compile error that names it.

tools/gen_themes.zig reads helix .toml and zed .json out of vendor/themes and
emits one .zig each; build.zig reads that directory, so adding a theme is
dropping a file in. Output goes to the build cache rather than the tree, so zig
owns the freshness check and a deleted source cannot leave a stale theme
behind. Vendored, not read from the genizah: the build stays offline. A source
it cannot map is a hard error naming the file and the key, never a silently
black-on-black theme.

ThemeSel is the clever half. Traits gained an `executes` column, so n/N over
that buffer hands the whole line to Exec instead of the leading word to Look —
both arms the ordinary builtin, so a stepped row does exactly what the matching
mouse button on it would. Stepping the list previews each theme live. The trait
is a pane property, not an output-pane branch, so any pane whose lines are
commands can opt in.

Goldens: leader gains SPC t t; theme's fourth NextColor no longer wraps to
helix because the ring is fifteen long. New: themesel.

1 files changed, 32 insertions, 32 deletions

diff --git a/test/snapshots/theme.golden b/test/snapshots/theme.golden
index 520258ff..c4a5a6d9 100644
--- a/test/snapshots/theme.golden
+++ b/test/snapshots/theme.golden
@@ -246,7 +246,7 @@
 |27: 0-99 d,#ffffea,
 |28: 0-99 d,#ffffea,
 |29: 0-99 d,#ffffea,
-== snap helix-again grid=100x30 cursor=4,4
+== snap generated grid=100x30 cursor=4,4
 |Kill Newcol Tutor Debug NextColor Dump Find Grep Help
 |  NOR /tmp/pardes-snap/theme/cwd Del                NOR /tmp/pardes-snap/theme/cwd Del
 |
@@ -277,34 +277,34 @@
 |
 |
 |
-== style helix-again
-|0: 0-52 #949494,#121212, 53-99 d,#121212,
-|1: 0-1 d,#626262, 2-35 #949494,#121212, 36-49 d,#121212, 50-51 d,#262626, 52-85 #949494,#121212, 86-99 d,#121212,
-|2: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|3: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|4: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|5: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|6: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|7: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|8: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|9: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|10: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|11: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|12: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|13: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|14: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|15: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|16: 0-1 d,#262626, 2-35 #949494,#121212, 36-49 d,#121212, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|17: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|18: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|19: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|20: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|21: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|22: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|23: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|24: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|25: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|26: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|27: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|28: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
-|29: 0-1 d,#444444, 2-49 #bdbdbd,#080808, 50-51 d,#444444, 52-99 #bdbdbd,#080808,
+== style generated
+|0: 0-52 #8a8986,#313337, 53-99 d,#313337,
+|1: 0-1 d,#5ac1fe, 2-35 #8a8986,#313337, 36-49 d,#313337, 50-51 d,#3f4043, 52-85 #8a8986,#313337, 86-99 d,#313337,
+|2: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|3: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|4: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|5: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|6: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|7: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|8: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|9: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|10: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|11: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|12: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|13: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|14: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|15: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|16: 0-1 d,#3f4043, 2-35 #8a8986,#313337, 36-49 d,#313337, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|17: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|18: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|19: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|20: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|21: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|22: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|23: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|24: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|25: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|26: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|27: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|28: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,
+|29: 0-1 d,#bfbdb6, 2-49 #bfbdb6,#0d1016, 50-51 d,#bfbdb6, 52-99 #bfbdb6,#0d1016,