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>

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

@@ -1,30 +1,34 @@
 import { useState, useEffect } from 'react';
-
-declare global {
-  interface Window {
-    __MCP_DATA__?: unknown;
-  }
-}
+import { App } from '@modelcontextprotocol/ext-apps';
 
 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;
-    }
+    const app = new App();
 
-    // 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
+    app.ontoolresult = (result: any) => {
+      // The host pushes tool result content; parse the first text item as JSON
+      if (result?.content) {
+        const textItem = Array.isArray(result.content)
+          ? result.content.find((c: any) => c.type === 'text')
+          : null;
+        if (textItem?.text) {
+          try {
+            setData(JSON.parse(textItem.text) as T);
+          } catch {
+            // Not JSON — use raw text as-is
+            setData(textItem.text as unknown as T);
+          }
+        }
       }
-    }
+    };
+
+    app.connect();
+
+    return () => {
+      app.close();
+    };
   }, []);
 
   return data;