fix: apply title templates to active articles

[bao-cn]

Summary

Make configured title templates take effect while reading articles with cat and less.

Implementation

• Apply the configured template when an article becomes active.
• Restore the default site title when article reading ends.
• Keep initial layout metadata consistent with the configured site title.
• Add template rendering and fallback tests.

Behavior and compatibility

Article pages now update document.title according to the configured template. This PR depends on feat/cookie-notice because both touch terminal and site configuration code.

Risk

The main risk is leaving a stale article title after navigation; title reset behavior is included in the implementation and tests.

Verification

npx prettier --check .
npm run lint
npx tsc --noEmit --incremental false
npm test
npm run build

All checks passed, including browser interaction checks.

Checklist

• The change is focused.
• Tests and bilingual documentation are updated.
• Visible title behavior was manually verified.