Replace symmetric HS256 JWT verification with asymmetric RS256 using JWKS.
Backend now fetches and caches public keys from Supabase's JWKS endpoint
instead of using a shared secret.
- Add cryptography dependency for RS256 support
- Use PyJWKClient to fetch/cache JWKS from {SUPABASE_URL}/.well-known/jwks.json
- Remove SUPABASE_JWT_SECRET from config, docker-compose, deploy workflow, .env
- Update tests to use RS256 tokens with mocked JWKS client
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
