Add Quickstart guide for building MCP Apps

Introduces a step-by-step tutorial covering:
- Project setup with Vite and TypeScript
- Server creation with tool + resource registration
- UI development using the App SDK
- Testing with basic-host

Also updates README to link to the guide and configures
typedoc to include it in generated documentation.

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

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

typedoc.json

@@ -1,5 +1,6 @@
 {
   "$schema": "https://typedoc.org/schema.json",
+  "projectDocuments": ["docs/quickstart.md"],
   "entryPoints": [
     "src/app.ts",
     "src/app-bridge.ts",