feat: MCP Apps - rich HTML UIs for tool results (#573)

* 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>

---------

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

ui-apps/src/shared/hooks/useToolData.ts

@@ -0,0 +1,31 @@
+import { useState, useEffect } from 'react';
+
+declare global {
+  interface Window {
+    __MCP_DATA__?: unknown;
+  }
+}
+
+export function useToolData<T>(): T | null {
+  const [data, setData] = useState<T | null>(null);
+
+  useEffect(() => {
+    // Try window.__MCP_DATA__ first (injected by host)
+    if (window.__MCP_DATA__) {
+      setData(window.__MCP_DATA__ as T);
+      return;
+    }
+
+    // Try embedded script tag
+    const scriptEl = document.getElementById('mcp-data');
+    if (scriptEl?.textContent) {
+      try {
+        setData(JSON.parse(scriptEl.textContent) as T);
+      } catch {
+        // Ignore parse errors
+      }
+    }
+  }, []);
+
+  return data;
+}