refactor(theme): consolidate near color values

[limityan]

Summary

• Consolidate highly similar theme color values across token contracts, builtin theme presets, runtime fallbacks, Monaco/editor, Mermaid, terminal, and mobile-web theme presets.
• Add a small mobile theme preset helper for repeated alpha/ramp/shadow construction while preserving the exact exported theme key sets and theme-specific blur/high-ramp values.
• Refresh generated startup theme projections, prompt snapshots, governance baselines, and the theme optimization design doc with the new metrics.

Metrics

• Web UI audit unique colors: 547 -> 498.
• Web UI color occurrences: 760 -> 722.
• Specialized color-domain near pairs: 324 -> 195.
• Specialized indistinguishable near pairs: 1 -> 0.
• Component/non-token raw colors, fallback vars, unresolved CSS vars, token-equivalent app literals: all remain 0.

Risk and boundaries

• No theme token keys were removed. Mobile darkTheme and lightTheme both remain 148 keys with 0 missing and 0 added keys versus the previous presets.
• Mobile theme helper generation preserves the previous blur values and the 700/800 ramp values that were based on each palette's stronger 600 color.
• Merges are limited to near alpha/surface values and specialized rendering domains where the values are highly similar or non-adjacent in the product UI.
• Remaining near pairs are still tracked in the governance baseline instead of being force-merged across adjacent surface hierarchy or identity palettes.
• Rust-side files in this PR are generated theme projections only; TS theme presets remain the source of truth.

Verification

• git diff --check gcwing/main..HEAD
• pnpm run theme:color-audit
• pnpm run generate-startup-theme-bootstrap -- --check
• pnpm run type-check:web
• pnpm run type-check:mobile-web
• pnpm run theme:color-audit:test
• pnpm run theme:visual-contract
• pnpm --dir src/web-ui run test:run
• pnpm run build:web
• Mobile theme key/value coverage script: darkTheme and lightTheme each 148 -> 148, missing=0, added=0; blur and 700/800 ramp values unchanged.