revert(theme): drop Dimidium as a built-in, use stock theme import

[deanjstone]

Summary

• Removes Dimidium as a compiled-in built-in theme, reverting the source half of #24.
• Dimidium moves to a custom theme imported through stock T3 Code (Settings → Appearance → Import), using a file generated by the repo's own serializeThemeFile.
• Takes the fork's theme divergence to zero source files.

Why

Preference for stock capability over fork-level divergence. Upstream already ships a theme import path, so carrying a palette in source was solving a problem the app solves itself.

This does not give back what #21 bought. index.css still carries no palette, so the conflict surface that motivated the port — 6 of the 21 conflicts in the 1295-commit sync — stays closed. The fork now carries less theme code than before #24, not more.

Revert fidelity

Five of six files return to matching upstream/main byte-for-byte:

File	State
packages/shared/src/themePalettes.ts	matches upstream
apps/mobile/generated-uniwind-theme-names.json	matches upstream
apps/mobile/uniwind-types.d.ts	matches upstream
apps/mobile/scripts/generate-uniwind-themes.test.ts	matches upstream
apps/mobile/src/lib/mobileThemeRuntime.test.ts	matches upstream
apps/mobile/generated-uniwind-themes.css	pure 250-line deletion, exactly reversing #24

Generated artefacts were regenerated via vp run --filter @t3tools/mobile generate and the uniwind generate-artifacts CLI, not hand-edited.

Kept deliberately

The --info/--success block in index.css (21 lines). Upstream deliberately keeps success, info, provider and channel identity colours outside the themeable role set, so no imported theme can carry them. These four roles are the one part stock genuinely cannot express.

Known cost

Dimidium is no longer available in the React Native mobile app. MOBILE_THEME_IDS enumerates built-ins only and the mobile app has no custom-theme support at all (confirmed: zero references to the custom-theme storage key under apps/mobile/src). The iPhone PWA is unaffected — it runs the web bundle, which supports imported themes.

Side effect: the theme file becomes importable here

A theme file is generated at ~/dimidium.json (untracked). While dimidium was a built-in it could not be imported into this fork — BUILT_IN_THEME_IDS feeds RESERVED_THEME_IDS, and parseThemeFile throws The theme id "dimidium" is reserved. This PR frees the id.

Note the file carries the post-fix values, including #24's WCAG correction (placeholder was 4.07:1 light / 3.23:1 dark, now 4.60:1 in both) — so the imported theme is the accessible version, not the original palette.

Test plan

• typecheck — exit 0, 0 errors
• vp check — exit 0, 0 errors (593 pre-existing warnings)
• Full mobile suite — 1230/1230, run from apps/mobile so the count matches CI's rather than an over-narrow filter
• Not verified: importing ~/dimidium.json through the UI after merge, and its appearance in light/dark

Re-opens #21.

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.4 KiB	13.5 KiB	+90 B (+0.7%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−3 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+93 B (+1.4%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	57.0 KiB	+822 B (+1.4%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.6 KiB	+59 B (+0.4%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	−5 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+64 B (+1.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.9 KiB	+88 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: eea8c23 · PR result: b64d8a0 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.