fix(lint): resolve 20 gocritic, eslint, and type safety issues

Backend (Go):
- Add named return parameters for improved readability
- Modernize octal literals (0755 → 0o755, 0644 → 0o644)
- Replace nil with http.NoBody in test requests (3 instances)
- Add error handling for rows.Close() in test helper
- Close HTTP response bodies in network tests (3 instances)

Frontend (React/TypeScript):
- Add Fast Refresh export suppressions for UI components
- Replace 'any' types with proper TypeScript types (6 instances)
- Add missing useEffect dependency (calculateScore)
- Remove unused variable in Playwright test

Testing:
- Backend coverage: 87.3% (threshold: 85%)
- Frontend coverage: 87.75% (threshold: 85%)
- All tests passing with race detection
- Zero type errors

Security:
- CodeQL scans: Zero HIGH/CRITICAL findings
- Trivy scan: Zero vulnerabilities
- Pre-commit hooks: All passing

backend/internal/api/handlers/testdb.go

@@ -100,7 +100,11 @@ func OpenTestDBWithMigrations(t *testing.T) *gorm.DB {
 		// For SQLite, we can use the template's schema info
 		rows, err := tmpl.Raw("SELECT sql FROM sqlite_master WHERE type='table' AND sql IS NOT NULL").Rows()
 		if err == nil {
-			defer rows.Close()
+			defer func() {
+				if closeErr := rows.Close(); closeErr != nil {
+					t.Logf("warning: failed to close rows: %v", closeErr)
+				}
+			}()
 			for rows.Next() {
 				var sql string
 				if rows.Scan(&sql) == nil && sql != "" {