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/crawl-progress-migration.sql

@@ -0,0 +1,21 @@
+-- Add new columns for improved crawl progress tracking
+ALTER TABLE crawl_sessions 
+ADD COLUMN IF NOT EXISTS total_urls INTEGER DEFAULT 0,
+ADD COLUMN IF NOT EXISTS processed_urls INTEGER DEFAULT 0,
+ADD COLUMN IF NOT EXISTS progress_percentage INTEGER DEFAULT 0,
+ADD COLUMN IF NOT EXISTS current_url TEXT;
+
+-- Update existing sessions to use new columns (map old data)
+UPDATE crawl_sessions 
+SET 
+  total_urls = pages_discovered,
+  processed_urls = pages_processed,
+  progress_percentage = CASE 
+    WHEN pages_discovered > 0 THEN ROUND((pages_processed::float / pages_discovered::float) * 100)
+    ELSE 0 
+  END
+WHERE total_urls IS NULL OR total_urls = 0;
+
+-- Add index for better performance
+CREATE INDEX IF NOT EXISTS idx_crawl_sessions_status ON crawl_sessions(status);
+CREATE INDEX IF NOT EXISTS idx_crawl_sessions_website_status ON crawl_sessions(website_id, status);