Summary

Adds full MCP Apps support - interactive UIs rendered from MCP server tools inside the Chat UI, with end-to-end metadata passthrough and resource proxying through the MCP Gateway.

/claim #1301

Resolves #1301

Changes

Backend (12 files)

• Schema: Added meta jsonb column to tools table (migration 0187)
• MCP Gateway passthrough: Fixed tools/list to return _meta and annotations from persisted tool.meta instead of hardcoded {}
• Resource handlers: Added resources/list and resources/read to MCP Gateway server for ui:// scheme resources
• REST endpoint: Added POST /:profileId/resources/read for frontend to fetch resource HTML
• Meta persistence: Updated connectAndGetTools, getToolsFromServer, syncToolsForCatalog, bulkCreateToolsIfNotExists, and all callers to propagate meta
• McpClient.readResource(): New method to proxy ui:// resource reads to upstream MCP servers
• Catalog seeds: Added n8n-mcp and excalidraw-mcp entries

Frontend (2 files)

• McpAppRenderer: New sandboxed iframe component with AppBridge JSON-RPC protocol (resize, getToolOutput)
• Chat integration: Detects tools with _meta.ui.resourceUri, renders interactive iframe alongside tool output

Tests

• Meta field persistence and update detection in syncToolsForCatalog

Docs

• New platform-mcp-apps.md documentation page

Architecture

User -> Chat UI -> MCP Gateway -> Upstream MCP Server
                      |
                tools/list (with _meta.ui.resourceUri)
                tools/call -> tool result
                resources/read -> HTML content -> sandboxed iframe

Tested with

• n8n-mcp (requires N8N_API_KEY + N8N_BASE_URL)
• excalidraw-mcp (no auth required)