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/package.json

@@ -23,20 +23,20 @@
   },
   "private": true,
   "dependencies": {
-    "@angular/common": "^20.3.0",
-    "@angular/compiler": "^20.3.0",
-    "@angular/core": "^20.3.0",
-    "@angular/forms": "^20.3.0",
-    "@angular/platform-browser": "^20.3.0",
-    "@angular/router": "^20.3.0",
+    "@angular/common": "^19.0.0",
+    "@angular/compiler": "^19.0.0",
+    "@angular/core": "^19.0.0",
+    "@angular/forms": "^19.0.0",
+    "@angular/platform-browser": "^19.0.0",
+    "@angular/router": "^19.0.0",
     "rxjs": "~7.8.0",
     "tslib": "^2.3.0",
     "zone.js": "~0.15.0"
   },
   "devDependencies": {
-    "@angular/build": "^20.3.5",
-    "@angular/cli": "^20.3.5",
-    "@angular/compiler-cli": "^20.3.0",
+    "@angular/build": "^19.0.0",
+    "@angular/cli": "^19.0.0",
+    "@angular/compiler-cli": "^19.0.0",
     "@types/jasmine": "~5.1.0",
     "jasmine-core": "~5.9.0",
     "karma": "~6.4.0",
@@ -44,6 +44,6 @@
     "karma-coverage": "~2.2.0",
     "karma-jasmine": "~5.1.0",
     "karma-jasmine-html-reporter": "~2.1.0",
-    "typescript": "~5.9.2"
+    "typescript": "~5.8.0"
   }
 }