refactor: compress cross-surface theme tokens

[limityan]

Summary

• Extend theme color governance from shared web UI to Mobile Web and Installer, including root-specific baselines, dynamic CSS var family ownership, and updated architecture documentation in docs/architecture/theme-token-optimization.md.
• Compress Mobile Web and Installer token surfaces by removing unused ramps/fallbacks/aliases, replacing raw component colors with existing semantic/surface tokens, and narrowing Installer accent runtime stops to the keys actually consumed.
• Consolidate repeated Monaco passive selection colors and keep cross-root audits from treating mobile/installer-owned dynamic keys as stale in web-ui-only checks.
• Keep Installer frontend/backend connection-test message codes aligned with the current adapter enum so the installer crate compiles against latest main.

Impact

• web-ui audit: 0 app raw colors, 0 fallback vars, 0 unresolved vars; editor occurrences lowered from 55 to 52.
• mobile-web audit: 37 total color occurrences, 35 unique colors, 1 intentional app UI literal (#fff for the image-remove control over black overlay), 0 fallback/unresolved/non-contract keys.
• installer audit: 203 total color occurrences, 147 unique colors, 0 app UI raw colors, 0 fallback/unresolved/non-contract keys; runtime dynamic families reduced to accent/purple only.
• governance docs now state the cross-root ownership model and require theme:color-audit:all for implementation PRs touching theme/runtime surfaces.

Verification

• pnpm run theme:color-audit:test
• pnpm run theme:color-audit:all
• pnpm run theme:visual-contract
• pnpm run lint:web
• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run
• pnpm run type-check:mobile-web
• pnpm run build:mobile-web (passes with existing Vite chunk-size warning)
• pnpm --dir BitFun-Installer run type-check
• pnpm --dir BitFun-Installer exec vite build
• cargo check --manifest-path BitFun-Installer/src-tauri/Cargo.toml
• git diff --check gcwing/main...HEAD

Risk Notes

• Theme personality colors in adjacent theme presets remain distinct; only unused or non-adjacent high-similarity/component literals were collapsed.
• The remaining Mobile Web #fff is intentionally retained for the image remove button because existing theme foreground tokens are not safe over a black thumbnail overlay in both light and dark themes.
• The final review tightened the Mobile Web baseline with cssVarDefinitions.nonContractCssPrivateUnique: 0 so private CSS var drift is guarded like web-ui and installer.
• A full installer packaged build was attempted earlier and timed out locally; the PR is validated with module-level TypeScript, Vite, and Rust checks instead.