Implement comprehensive repository management system for WHOOSH

- Add database migrations for repositories, webhooks, and sync logs tables
- Implement full CRUD API for repository management
- Add web UI with repository list, add form, and management interface
- Support JSONB handling for topics and metadata
- Handle nullable database columns properly
- Integrate with existing WHOOSH dashboard and navigation
- Enable Gitea repository monitoring for issue tracking and CHORUS integration

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

migrations/003_add_repositories_table.down.sql

@@ -0,0 +1,9 @@
+-- Rollback repository monitoring tables
+
+-- Remove new column from tasks table
+ALTER TABLE tasks DROP COLUMN IF EXISTS repository_id;
+
+-- Drop tables in reverse order
+DROP TABLE IF EXISTS repository_sync_logs;
+DROP TABLE IF EXISTS repository_webhooks;  
+DROP TABLE IF EXISTS repositories;