feat: add Angular workspace with demo app and library build

- Restructure into standard Angular library workspace
- Library source in projects/ngx-pretext-table/
- Demo app in src/ using PretextVirtualScrollDirective
- Switch @chenglou/pretext dependency to npm registry (^0.0.4)
- Fix moduleResolution to "bundler" for Angular 17 compatibility

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tsconfig.app.json

@@ -0,0 +1,9 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "outDir": "./out-tsc/app",
+    "types": []
+  },
+  "files": ["src/main.ts"],
+  "include": ["src/**/*.d.ts"]
+}