feat(theme): add Catppuccin Mocha and Macchiato interface themes

[zuhayermasud]

What?

Adds Catppuccin as an interface (chrome) theme — sidebar, panels, borders, text hierarchy, and accent color for the whole app — not just editor syntax highlighting (already shipped in #213). Ships Mocha and Macchiato; Latte and Frappé are both intentionally excluded (see Why).

Why?

Latte is skipped because Atlas's interface theme system is dark-theme-only by design (see the file header in themes.ts).

Frappé is skipped for a more interesting reason: its base (#303446) is light enough that several already-shipped editor themes' comment tokens — tuned only against Atlas's near-black interface bases — drop below themes.test.ts's contrast floor when tested against it. Fixing this for the default atlas theme specifically turned out to be mathematically unworkable: atlas's comment color needs to clear AA (4.5:1) against Frappé's base and stay >1.5:1 apart in luminance from atlas's own keyword color — and those two constraints together only have solutions that either push the keyword to a washed-out near-white pastel, or push the comment above the theme's own body-text brightness. Rather than force a bad-looking compromise into the default theme everyone sees, Frappé is left out; Mocha and Macchiato don't have this problem.

How?

Registers two AtlasTheme entries in ATLAS_THEMES. Role mapping follows Catppuccin's own published style guide (Base = background pane, Crust/Mantle = secondary panes darker than base, Surface 0/1/2 = raised elements, Text/Subtext/Overlay = the text hierarchy, "On Accent" = Base, mauve as the accent — matching the already-shipped editor themes for family consistency). This deliberately crosses Atlas's own convention of every surface only ever rising above base, since Catppuccin's Crust/Mantle are explicitly darker.

Since every AtlasTheme.base feeds the cross-theme contrast suite in src/features/editor/themes/themes.test.ts, adding these two lighter bases required minimal, computed comment-color nudges in four already-shipped editor themes (atlas-mono, one-dark, monokai, tokyo-night) — the default atlas theme needed no change at all.

No other file needs to change to make these selectable: apply-atlas-theme.ts, atlas-themes-settings.tsx, and the settings store are all fully data-driven off ATLAS_THEMES.

Verification

• vitest run — full suite, 1048 tests pass, including the cross-theme contrast suite (every editor syntax theme against every interface base, including the two new Catppuccin ones)
• tsc --noEmit clean
• Confirmed no hardcoded theme-id checks exist outside src/features/theme (grepped the full src tree)

Checklist

• Targets the current dev branch (0.3.1)
• New behaviour has a test; the existing cross-theme contrast suite automatically covers the new registry entries
• Run the app and use the change in a window