Add an `mcp_app_demo` tool/resource preset — a self-contained MCP App widget
that exercises size-changed, ui/message, log notifications, and host-context
rendering with no external server. Requires plumbing an optional `_meta` field
through the composable test server's `ToolDefinition` and `ResourceDefinition`
so clients can read tool-level `_meta.ui.resourceUri` and resource-level
`_meta.ui.csp`.
- composable-test-server: optional `_meta` on ToolDefinition/ResourceDefinition,
passed through to registerTool config and the resource content item.
- test-server-fixtures: `createMcpAppDemoTool()`, `createMcpAppDemoResource()`,
inline `MCP_APP_DEMO_HTML` widget; wired into getDefaultServerConfig.
- preset-registry: `mcp_app_demo` tool + `mcp_app_demo_widget` resource presets.
- integration test asserting the `_meta` plumbing end-to-end.
Wave 1 of PR #1510 decomposition.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3fTN8H3R8YV4yUGvZjYnX
0d50b908a3