Add a feature-flag service backed by Postgres + in-memory cache

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox campaign. Read flags from a flags table at startup; cache in-process and refresh every 30s.

Requirements and Context

• GET /api/admin/flags
• Per-flag boolean + variant
• Cache TTL
• Tests cover
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feature/feature-flags

2. Implement changes
   • src/services/featureFlags.ts (new)
   • drizzle/migrations/0014_flags.sql (new)
   • src/routes/admin/flags.ts (new)
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

feat: feature flag service

Acceptance Criteria

• Reads + cache
• CRUD works
• Variant supported
• Tests pass

Guidelines

• Minimum 90% test coverage on changed lines
• Input validation at the boundary; standardized error envelope
• Structured logging with correlation IDs
• Clear documentation and inline comments
• Timeframe: 96 hours