feat: persist community events to the database

[Arowolokehinde]

Summary

Replaces the in-memory events array in community.controller.ts with proper pg pool queries backed by a new community_events table.

• Add migration 022_community_events.sql: community_events table with a CHECK constraint enforcing valid event types, and B-tree indexes on type and date for O(log n) filtering and sort-free ordering.
• Add 022_community_events.undo.sql for clean rollback.
• Rewrite getEvents/createEvent as async handlers using pool.query(), structured logging via logger.child(), and input validation with asNonEmptyString() matching the sponsors.controller.ts pattern.
• Drop the two hardcoded placeholder events; seed data does not belong in production application code or migrations.
  Closes feat: persist community events to the database instead of an in-memory array #1004

Type of Change

• Bug fix
• New feature
• Smart contract change
• Documentation
• Breaking change
• Other (please describe)

Checklist

• Tests added or updated
• No hardcoded secrets or private keys
• If contract change: cargo test passes
• If frontend change: npm run typecheck passes
• If backend change: npm test passes
• Related issues linked (Closes #...)
• Self-review completed
• Code follows project style guidelines

Screenshots (if applicable)

Testing

Additional Notes