fix: align MCP Apps with official ext-apps spec (#574)

* feat: add MCP Apps with rich HTML UIs for tool results

Add MCP Apps infrastructure that allows MCP hosts like Claude Desktop
to render rich HTML UIs alongside tool results via `_meta.ui` and the
MCP resources protocol.

- Server-side UI module (src/mcp/ui/) with UIAppRegistry, tool-to-UI
  mapping, and _meta.ui injection into tool responses
- React + Vite build pipeline (ui-apps/) producing self-contained HTML
  per app using vite-plugin-singlefile
- Operation Result UI for workflow CRUD tools (create, update, delete,
  test, autofix, deploy)
- Validation Summary UI for validation tools (validate_node,
  validate_workflow, n8n_validate_workflow)
- Shared component library (Card, Badge, Expandable) with n8n dark theme
- MCP resources protocol support (ListResources, ReadResource handlers)
- Graceful degradation when ui-apps/dist/ is not built
- 22 unit tests across 3 test files

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

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

* test: improve MCP Apps test coverage and add security hardening

- Expand test suite from 22 to 57 tests across 3 test files
- Add UIAppRegistry.reset() for proper test isolation between tests
- Replace some fs mocks with real temp directory tests in registry
- Add edge case coverage: empty strings, pre-load state, double load,
  malformed URIs, duplicate tool patterns, empty HTML files
- Add regression tests for specific tool-to-UI mappings
- Add URI format consistency validation across all configs
- Improve _meta.ui injection tests with structuredContent coexistence
- Coverage: statements 79.4% -> 80%, lines 79.4% -> 80%

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

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

* fix: align MCP Apps with official ext-apps spec

Update URI scheme from n8n-mcp://ui/ to ui://n8n-mcp/ per MCP spec.
Move _meta.ui.resourceUri to tool definitions (tools/list) instead of
tool call responses. Rewrite UI apps hook to use @modelcontextprotocol/ext-apps
App class instead of window.__MCP_DATA__.

Conceived by Romuald Czlonkowski - https://www.aiadvisors.pl/en
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,21 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.34.1] - 2026-02-07
+
+### Changed
+
+- **MCP Apps: Align with official ext-apps spec** for Claude Desktop/web compatibility
+  - URI scheme changed from `n8n-mcp://ui/{id}` to `ui://n8n-mcp/{id}` per MCP ext-apps spec
+  - `_meta.ui.resourceUri` now set on tool definitions (`tools/list`) instead of tool call responses
+  - `UIMetadata.ui.app` renamed to `UIMetadata.ui.resourceUri`
+  - Added `_meta` field to `ToolDefinition` type
+  - Added `UIAppRegistry.injectToolMeta()` method for enriching tool definitions
+  - UI apps now use `@modelcontextprotocol/ext-apps` `App` class instead of `window.__MCP_DATA__`
+  - Updated `ReadResource` URI parser to match new `ui://` scheme
+
+Conceived by Romuald Czlonkowski - https://www.aiadvisors.pl/en
+
 ## [2.34.0] - 2026-02-07
 
 ### Added