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

frontend/src/components/ui/Button.tsx

@@ -107,4 +107,5 @@ const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
 )
 Button.displayName = 'Button'
 
+// eslint-disable-next-line react-refresh/only-export-components
 export { Button, buttonVariants }

frontend/src/components/ui/Label.tsx

@@ -41,4 +41,5 @@ const Label = React.forwardRef<HTMLLabelElement, LabelProps>(
 )
 Label.displayName = 'Label'
 
+// eslint-disable-next-line react-refresh/only-export-components
 export { Label, labelVariants }