feat(web): add color theme presets

[NightWatcher314]

Summary

• add 17 palette presets without changing layout or appearance modes
• keep presets independent from System / Light / Dark / OLED appearance
• preserve per-appearance custom-color and chat-surface overrides above preset values
• integrate the picker with the latest responsive Display settings page
• sync palette changes across tabs and apply the palette background during early boot

Implementation notes

This supersedes #964 with a fresh branch based on current main, after the responsive settings redesign in #1027. It preserves the fixes from the earlier bot review:

• preset -> custom color -> chat surface override layering
• cross-tab updates even when Settings is not mounted
• early boot background and browser theme-color synchronization

OLED intentionally uses each preset's dark palette while retaining OLED as a separate appearance option when the default palette is selected.

Validation

• bun typecheck
• targeted web tests: 39 passed
• bun run build:web
• full CLI tests: 1250 passed
• full hub tests: 482 passed, 3 skipped
• full web suite has one pre-existing environment failure in markdown-a.test.tsx: jsdom rejects Bun's experimental localStorage as StorageEvent.storageArea; unrelated targeted rerun reproduces it on upstream code

Closes #963

[github-actions]

Findings
None.

Summary
Review mode: initial
No high-confidence issues found in the added/modified lines. Residual risk: review was limited to static inspection of the web theme/color changes and related initialization paths.

Testing
Not run (automation review; did not execute PR code).

HAPI Bot