feat: add app homepage resource metadata

[Chipagosfinest]

What changed

• adds optional homepage metadata to McpUiResourceMeta
• regenerates the Zod and JSON schemas
• documents the field in the draft MCP Apps specification and resource examples
• verifies registerAppResource preserves the metadata

Why

ui.domain configures a host-assigned sandbox origin; it is not the app's public homepage. MCP servers and public app sites may also live at different locations, so hosts currently have no portable metadata they can use to help users learn more about or return to an app.

The documentation explicitly treats homepage as an untrusted external link. It does not grant navigation permission or establish destination trust; hosts retain their normal URL validation, policy, and consent behavior.

Closes #703.

Validation

• bun test src/server/index.test.ts src/generated/schema.test.ts
• npm run build
• npm run prettier
• npm exec typedoc -- --treatValidationWarningsAsErrors --emit none
• repository pre-commit hook: npm run build:all