feat(feeds): add XRPC handler for getCommunity endpoint master
Implements the HTTP handler layer for social.coves.feed.getCommunity: - GetCommunityHandler: XRPC endpoint handler with proper validation - Query parameter parsing: community, sort, limit, cursor - Error handling: Proper XRPC error responses (InvalidRequest, NotFound) - Route registration: Public endpoint (no auth required for reading) Security: - Input validation for all query parameters - Limit clamping (max 100 posts per request) - Community existence verification - No sensitive data exposure in error messages Handler flow: 1. Parse and validate query parameters 2. Call feed service 3. Transform to XRPC response format 4. Return JSON with proper headers This implements the read path for community feeds per atProto patterns. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>