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.

flake.nix

@@ -96,6 +96,67 @@
           '';
         };
 
+        # Apps - Scripts that can be run with `nix run`
+        apps = {
+          # Unified linting for all code
+          lint = {
+            type = "app";
+            program = "${pkgs.writeShellScript "lint" ''
+              set -e
+              cd ${self}
+              
+              # Backend Python linting
+              echo "🔍 Linting backend Python code..."
+              cd backend
+              ${pkgs.ruff}/bin/ruff check --no-cache app/
+              ${pkgs.ruff}/bin/ruff format --check app/
+              cd ..
+              
+              # Frontend linting (if node_modules exists)
+              if [ -d "frontend/node_modules" ]; then
+                echo ""
+                echo "🔍 Linting frontend TypeScript/Svelte code..."
+                cd frontend
+                npm run lint
+                npx prettier --check src/
+                npm run check
+                cd ..
+              else
+                echo "⚠  Frontend node_modules not found, run 'npm install' first"
+              fi
+              
+              echo ""
+              echo "✅ All linting checks passed!"
+            ''}";
+          };
+          
+          # Auto-fix linting issues
+          lint-fix = {
+            type = "app";
+            program = "${pkgs.writeShellScript "lint-fix" ''
+              set -e
+              cd ${self}
+              
+              echo "🔧 Auto-fixing backend Python code..."
+              cd backend
+              ${pkgs.ruff}/bin/ruff check --fix --no-cache app/
+              ${pkgs.ruff}/bin/ruff format app/
+              cd ..
+              
+              if [ -d "frontend/node_modules" ]; then
+                echo ""
+                echo "🔧 Auto-fixing frontend code..."
+                cd frontend
+                npx prettier --write src/
+                cd ..
+              fi
+              
+              echo ""
+              echo "✅ Auto-fix complete!"
+            ''}";
+          };
+        };
+
         # Package definitions (for production deployment)
         packages = {
           # Backend package