fix(mcp): harden MCP Apps host security and CJS compatibility

Reimplement the MCP Apps ui-meta helpers (RESOURCE_MIME_TYPE, getToolUiResourceUri,
isToolVisibilityModelOnly, isToolVisibilityAppOnly) in packages/api/src/mcp/apps.ts so
@librechat/api no longer imports the ESM-only @modelcontextprotocol/ext-apps from its CommonJS
build. ext-apps remains a client-only dependency, removing the require(ESM) boundary that throws
ERR_REQUIRE_ESM on Node versions without synchronous require(esm) support.

Add an mcpSettings.apps toggle (enabled unless explicitly false). Thread enableApps through
connection creation so the io.modelcontextprotocol/ui capability is advertised only when apps are
enabled, and gate the resource and app-tool-call routes with a requireMCPAppsEnabled middleware.

Authorize app-driven resources/read against the resources and templates a server advertises, so a
sandboxed app cannot proxy arbitrary uris. ui:// resources stay allowed and the check fails closed.

Render MCP apps in shared and search transcripts display-only by withholding the host-bound bridge
handlers and capabilities in read-only views, so an embedded app cannot call tools or read
resources with the viewer's auth while the stored tool result still renders.

packages/api/package.json

@@ -115,7 +115,6 @@
     "@keyv/redis": "^4.3.3",
     "@librechat/agents": "^3.2.44",
     "@librechat/data-schemas": "*",
-    "@modelcontextprotocol/ext-apps": "^1.7.4",
     "@modelcontextprotocol/sdk": "^1.29.0",
     "@opentelemetry/api": "^1.9.0",
     "@opentelemetry/instrumentation-express": "^0.56.0",