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.

2 files changed, 14 insertions, 8 deletions

diff --git a/docs/design.typ b/docs/design.typ
index 7a9cc5c7..5d6daad2 100644
--- a/docs/design.typ
+++ b/docs/design.typ
@@ -243,13 +243,19 @@ visible-range first), Save, open-at-line, undo/redo. Image: zstbi decode,
 kitty graphics when available, petscii matcher fallback (C64/terminal
 palettes, ascii glyph set toggle). Tutor: embedded text as file pane.
 
-*Chrome.* Themes helix (default; near-black page, chrome one grey-ramp step
-off it, colors lifted from the helix editor's own theme), dark, acme-light —
-the first two leave a child's ANSI palette native, acme-light resolves it onto
-the page so shell output stays readable on yellow. A theme owns the page, the
-tag bar, the gutter and the move box; the selection colors stay fixed because
-they encode which button you pressed. Colors toggles all recolor passes; Debug
-stats overlay; Dump writes state ZON.
+*Chrome.* One theme per `.zig` file, folded into the ring at comptime: ours
+first — helix (default; near-black page, chrome one grey-ramp step off it,
+colors lifted from the helix editor's own theme), dark, acme-light — then
+everything `tools/gen_themes.zig` exports at build time out of the vendored
+helix `.toml` and zed `.json` sources in `vendor/themes`. helix and dark leave
+a child's ANSI palette native; acme-light and the zed exports resolve it onto
+the page so shell output stays readable on a light one. A theme owns the page,
+the tag bar, the gutter and the move box; the selection colors stay fixed
+because they encode which button you pressed. `NextColor` walks the ring,
+`Theme <name>` jumps to one and `ThemeSel` (`SPC t t`) lists them all into an
+output buffer whose rows are those very commands — so n/N EXECUTE each row
+instead of looking it and stepping the list wears the themes. Colors toggles
+all recolor passes; Debug stats overlay; Dump writes state ZON.
 
 *Web (replay viewer parity).* Embedded dump; focus, border/move drags, wheel,
 scrollbar, Colors/NextColor, pinch, render scale, and link-LOOK opening a new
diff --git a/docs/helix-keys.md b/docs/helix-keys.md
index 8583dee0..36002eed 100644
--- a/docs/helix-keys.md
+++ b/docs/helix-keys.md
@@ -92,7 +92,7 @@ with a reason in `test/hxcases/waivers.jsonl`.
 | `Ctrl-w` + `h/j/k/l`/arrows | directional pane focus prefix — normal/tty modes only | pardes' own window handling (helix window mode skipped, section C). Runs the SAME `Left`/`Down`/`Up`/`Right` builtins `SPC w h/j/k/l` runs; kept alongside the leader because a pane in raw **tty** mode never sees `SPC` (the shell owns it), so this is the only keyboard way out of one. Insert mode owns `Ctrl-w` = delete-word-back, so a tag being TYPED into swallows it; from a tag in normal mode (`:`) it moves focus to the neighbour's BODY, while the bare letters `h/j/k/l` there move to its TAGLINE (next row) | pardes-specific |
 | `Alt-n` | new terminal below (any mode) | shadows helix `Alt-n` TS sibling-select — skipped anyway (tree-sitter) | pardes-specific |
 | `Alt-c` | move active terminal to a fresh column (any mode) | helix `Alt-c` is change-noyank; the pardes window op wins (do-not-touch contract). `Alt-d` + `i` covers the behavior | waived (`alt-c-window-op`) |
-| `Space` (normal, body) | the pardes LEADER: a key path from here runs a BUILTIN with no arguments — the same builtins the topbar and the tags hold. `SPC k` Kill, `SPC d` Del, `SPC f s` Save, `SPC f f` Find (fd over the pane's directory, results into `+Search`), `SPC f g` Grep (grep -R over the CONTENTS of every pane's directory, the ones another pane already covers dropped, rows relative to the asking pane's own directory, results into `+Search`; like Find it takes an ARGUMENT — `Grep foo` executed, or a selection chorded onto the word, searches that and skips the input), `SPC h t` Tutor, `SPC c n`/`SPC c d` Newcol/Delcol, `SPC t d/c/n/r` Debug/Colors/NextColor/Crt, `SPC t p/l/a` Petscii/Palette/Ascii (an image pane's renderer toggles — the words its tag used to spell out, so the bar stays a bar), `SPC s d`/`SPC s r` Dump/Restore, `SPC w h/j/k/l` Left/Down/Up/Right (directional pane focus — the `Ctrl-w` prefix's four moves as builtins), `SPC w t` Toggleterm (focus hops between the most recently focused document — file, image or `+Search`/`+Help` buffer — and the most recently focused terminal; the same key hops back). `?` at ANY depth opens the Help builtin listing what the prefix can still reach (`SPC ?` = all, `SPC h ?` = the docs group), into a `+Help` output buffer. The pending path shows at the right edge of the active pane's tag; Esc — or any unmapped key — abandons it | helix spends Space on pickers/LSP (section C); pardes has neither, and acme's builtins are what a leader is for. Enum-derived: the paths, the Help lines and the execute dispatch all fold out of one `Builtin` enum at comptime. Normal mode on a BODY only — tags are always insert, tty keys belong to the program | pardes-specific |
+| `Space` (normal, body) | the pardes LEADER: a key path from here runs a BUILTIN with no arguments — the same builtins the topbar and the tags hold. `SPC k` Kill, `SPC d` Del, `SPC f s` Save, `SPC f f` Find (fd over the pane's directory, results into `+Search`), `SPC f g` Grep (grep -R over the CONTENTS of every pane's directory, the ones another pane already covers dropped, rows relative to the asking pane's own directory, results into `+Search`; like Find it takes an ARGUMENT — `Grep foo` executed, or a selection chorded onto the word, searches that and skips the input), `SPC h t` Tutor, `SPC c n`/`SPC c d` Newcol/Delcol, `SPC t d/c/n/r` Debug/Colors/NextColor/Crt, `SPC t t` ThemeSel (the whole theme ring as `Theme <name>` rows in an output buffer — the one list whose rows are COMMANDS, so n/N execute each row instead of looking it and stepping is a live preview), `SPC t p/l/a` Petscii/Palette/Ascii (an image pane's renderer toggles — the words its tag used to spell out, so the bar stays a bar), `SPC s d`/`SPC s r` Dump/Restore, `SPC w h/j/k/l` Left/Down/Up/Right (directional pane focus — the `Ctrl-w` prefix's four moves as builtins), `SPC w t` Toggleterm (focus hops between the most recently focused document — file, image or `+Search`/`+Help` buffer — and the most recently focused terminal; the same key hops back). `?` at ANY depth opens the Help builtin listing what the prefix can still reach (`SPC ?` = all, `SPC h ?` = the docs group), into a `+Help` output buffer. The pending path shows at the right edge of the active pane's tag; Esc — or any unmapped key — abandons it | helix spends Space on pickers/LSP (section C); pardes has neither, and acme's builtins are what a leader is for. Enum-derived: the paths, the Help lines and the execute dispatch all fold out of one `Builtin` enum at comptime. Normal mode on a BODY only — tags are always insert, tty keys belong to the program | pardes-specific |
 | `/` then `n`/`N` (any pane) | pardes' own plain-substring search into a `+Search` output buffer, n/N walk the result rows and look them (EXPLICIT selections) | KEEP, do not touch; not in the corpus (helix `/` is regex search) | pardes-specific |
 | `n`/`N` (terminal panes, no search armed) | lookable-token motion over scrollback (EXPLICIT selections) | KEEP, do not touch | pardes-specific |
 | insert: printable text | file: real edit; terminal: typed run splice | | helix-verified (file) |