Improve community search with focused, paginated results

[drewmt]

Why

Community search stopped at eight matches per category, so members could not reach older conversations or additional people. This adds focused Posts, Spaces, People and Topics views with previous/next pages while keeping the overview useful.

What changed

• Query-preserving category links, stable ordering and bounded pagination without global result-count queries.
• Existing visibility and blocking rules applied before pagination on every request.
• A cleaner responsive search surface, useful empty states and browser Back/Forward support.
• Updated README screenshots for desktop, mobile and dark mode, plus the public search contract.

Validation

• Full local CI: 361 tests, 4,138 assertions, PHPStan, Pint, TypeScript, ESLint and Prettier passed after installing the exact committed lockfiles.
• Production frontend build passed.
• Browser checks covered page two, query reset, Back/Forward, empty-category and missing-page recovery, 320px/390px layouts and dark mode. No console errors or warnings.
• Screenshots use synthetic data in an isolated local SQLite database.

No new dependency, schema migration, API v1 change or production deployment.