feat: add unified linting scripts and git hooks for code quality enforcement

- Introduced `lint` and `lint-fix` applications in `flake.nix` for unified linting of backend (Python) and frontend (TypeScript/Svelte) code.
- Added `scripts/lint.sh` for manual linting execution.
- Created `scripts/install-hooks.sh` to set up git hooks for automatic linting before commits and optional tests before pushes.
- Updated `README.md` with instructions for using the new linting features and git hooks.

README.md

@@ -59,6 +59,56 @@ npm run dev
 - Backend API Docs: http://localhost:8000/docs
 - Backend Health: http://localhost:8000/health
 
+## Code Quality & Linting
+
+### Unified Linting (All Languages)
+
+```bash
+# Check all code (Python + TypeScript/Svelte)
+./scripts/lint.sh
+# OR using nix:
+nix run .#lint
+
+# Auto-fix all issues
+nix run .#lint-fix
+```
+
+### Git Hooks (Automatic)
+
+Install git hooks to run linting automatically:
+
+```bash
+./scripts/install-hooks.sh
+```
+
+This installs:
+- **pre-commit**: Runs linting before each commit
+- **pre-push**: Runs tests before push (optional)
+
+To skip hooks when committing:
+```bash
+git commit --no-verify
+```
+
+### Manual Linting
+
+**Backend (Python):**
+```bash
+cd backend
+ruff check app/          # Check for issues
+ruff check --fix app/    # Auto-fix issues  
+ruff format app/         # Format code
+```
+
+**Frontend (TypeScript/Svelte):**
+```bash
+cd frontend
+npm run lint             # ESLint check
+npm run check            # TypeScript check
+npx prettier --check src/  # Prettier check
+npx prettier --write src/  # Auto-format
+```
+
 ## Project Structure
 
 ```