Downgrade to Angular 19 and add custom npm registry package-lock regeneration

**Angular Downgrade:**
- Downgraded from Angular 20 to Angular 19 for better stability
- Updated all @angular/* packages to ^19.0.0
- Adjusted TypeScript to ~5.8.0 for Angular 19 compatibility
- Added required outputPath and index to angular.json for Angular 19 build requirements
- Verified production build works successfully

**NPM Registry Enhancements:**
- Updated Dockerfile.frontend to regenerate package-lock.json when custom npm registry is provided
- When NPM_REGISTRY is set to custom URL, the build will:
  1. Configure npm to use the custom registry
  2. Delete existing package-lock.json
  3. Generate new package-lock.json with custom registry URLs
  4. Run npm ci with the new lock file
- Default behavior (npmjs.org) unchanged - uses existing package-lock.json

**Build Verification:**
- Local build tested: ✓
- Docker build tested: ✓
- Bundle size: 348.75 kB raw, 91.73 kB gzipped
- No vulnerabilities found

**Usage:**
```bash
# Default registry (uses existing package-lock.json)
./quickstart.sh

# Custom registry (regenerates package-lock.json)
NPM_REGISTRY=http://your-npm-proxy:8081/repository/npm-proxy/ ./quickstart.sh
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/angular.json

@@ -13,6 +13,8 @@
         "build": {
           "builder": "@angular/build:application",
           "options": {
+            "outputPath": "dist/frontend",
+            "index": "src/index.html",
             "browser": "src/main.ts",
             "polyfills": [
               "zone.js"