Add theme overrides and local deployment

[DanielCuevas1208]

Summary

This pull request adds theme overrides and local deployment.

• Add configurable theme values for accent, radius, and font.
• Apply theme tokens to the generated CSS.
• Add a theme gallery page for comparing palettes.
• Add a versioned site manifest with theme details.
• Add local deploy sync with stale-file cleanup.
• Add commit-diff summaries and an RSS feed.

Review corrections

All review comments are resolved.

The page body uses the font token.
Project cards and panels use the radius token.
The publish path copies screenshots once.
Tests cover the generated CSS tokens.
Local deploy removes stale files before it copies the new site.

Validation

Run the test suite, type check, build, and generated-site tests.

npm run typecheck
npm run build
npm test

CI also runs the fixture demo, manifest verification, and deploy verification.

[DanielCuevas1208]

Do not merge this revision yet. The milestone is useful, but the generated theme does not apply two public settings. The CSS defines --font, but the page does not use it. The CSS defines --radius, but project cards still use a fixed 16 px radius. The publish path also copies screenshots twice. Connect both theme tokens to the rendered CSS, remove the duplicate copy step, and add tests for the generated CSS. Also define whether local deployment removes stale files before it copies the new site.