test(e2e,verify): enhance live API verification and dynamic port binding in E2E runner

- Update verify_counts.py to validate SQLite database records and live Go REST API endpoints directly
- Harden E2E test runner with dynamic free port binding (get_free_port) to prevent port collisions
- Add exact regex matching for dynamic (ƒ) and static (○) route table allocations
- Ignore root build binary artifacts in backend/.gitignore

backend/Makefile

@@ -21,6 +21,8 @@ seed: build
 	./$(BIN_DIR)/seed --db $(DB_PATH) --seed-dir seed/data
 
 export-content: build
+	@echo "⚠️ Notice: Frontend has migrated to real-time dynamic runtime fetching (force-dynamic)."
+	@echo "export-content is deprecated to prevent re-introducing static content data files."
 	./$(BIN_DIR)/export-content --db $(DB_PATH) --out-dir ../refer_landing_page/content
 
 fmt: