test: add stalker-mock-server and integrate with e2e tests

- Introduced `stalker-mock-server` with TypeScript configuration for local development and testing.
- Updated `playwright.config.ts` to run both Angular app and mock server in parallel during e2e tests.
- Created comprehensive e2e tests for Stalker portal functionality, including health checks, portal addition, and content loading.
- Added detailed architecture documentation for both `stalker-mock-server` and `xtream-mock-server`, outlining design decisions, data flow, and API protocols.
- Implemented `xtream-mock-server` to simulate Xtream Codes API for local development and testing, with corresponding e2e tests.
- Enhanced test isolation by resetting mock server state before each test run.

apps/stalker-mock-server/tsconfig.json

@@ -0,0 +1,16 @@
+{
+    "compilerOptions": {
+        "target": "ES2022",
+        "module": "CommonJS",
+        "moduleResolution": "node",
+        "lib": ["ES2022"],
+        "outDir": "../../dist/apps/stalker-mock-server",
+        "rootDir": "src",
+        "strict": true,
+        "esModuleInterop": true,
+        "skipLibCheck": true,
+        "resolveJsonModule": true
+    },
+    "include": ["src/**/*.ts"],
+    "exclude": ["node_modules", "dist"]
+}