refactor: flatten monorepo structure to backend/ frontend/ devops/

Rename subdirectories for a cleaner single-repo layout:
- website-monitoring-backend/  → backend/
- website-monitoring-frontend/ → frontend/
- website-monitoring-devops/   → devops/

Update all references in package.json scripts, CI workflows,
docker-compose, pre-commit hooks, and documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/supabase/migrations/20250813102542_add_missing_crawl_session_columns.sql

@@ -0,0 +1,8 @@
+-- Add missing columns to crawl_sessions table that the API expects
+-- Add total_urls and processed_urls columns that the API is trying to insert
+ALTER TABLE crawl_sessions ADD COLUMN IF NOT EXISTS total_urls INTEGER DEFAULT 0;
+ALTER TABLE crawl_sessions ADD COLUMN IF NOT EXISTS processed_urls INTEGER DEFAULT 0;
+
+-- Refresh schema cache to pick up new columns
+NOTIFY pgrst, 'reload schema';
+