Add Catppuccin built-in app theme (Latte light, Mocha dark)

[SawyerHood]

Summary

Adds Catppuccin as a new built-in app theme alongside the existing built-ins (default, nord, dracula, solarized, gruvbox).

• Light mode = Catppuccin Latte, dark mode = Mocha, accent = Mauve.
• Uses the official Catppuccin hexes and per-flavor ANSI terminal palettes.
• Unlike Nord (whose terminal colors are mode-independent), Latte and Mocha have different ANSI colors, so the --ansi-* / --ansi-bg-fg-* definitions live in both the light and dark selectors rather than being collapsed into one block.

Changes

Three core integration points:

• New apps/app/src/lib/themes/catppuccin.ts — exports catppuccinThemeCss (mirrors nord.ts).
• apps/app/src/lib/themes/index.ts — registers catppuccin in the builtInThemeCss record.
• packages/domain/src/app-theme.ts — adds "catppuccin" to appThemeIdSchema and a builtInThemes metadata entry.

The Settings picker (SettingsView.tsx), the SDK (theme.ts), and the bb theme CLI command all iterate over builtInThemes / BUILTIN_THEME_IDS, so they pick up the new theme automatically — confirmed, no changes needed.

Manual wiring beyond the three core files: two bb-cli skill docs (SKILL.md, references/theming.md) enumerate the built-in id list by hand in their bb theme set <id> docs, so catppuccin was appended to each.

Tests

• pnpm exec turbo run typecheck --filter=@bb/domain --filter=@bb/app — ✅ 2/2 passed. (The Record<Exclude<AppThemeId, "custom">, string> in index.ts now requires the catppuccin key, confirming the wiring.)
• pnpm exec turbo run test --filter=@bb/server -- appearance — ✅ 5/5 passed.

Risks

Low. Additive only — adds one palette and its metadata; no existing themes or behavior change.

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