Add the assistant: a chat that drives the MCP tools in-process

A provider set under Settings (OpenAI-compatible; key encrypted in
flow-data/ai.json) turns on an Assistant panel in the sidebar. Each turn runs
the FastMCP tools in-process as the person chatting, streams the rounds over
SSE and keeps one transcript per user. The panel floats on any screen and
shares the editor's lane: a settings panel keeps the top half, the chat the
bottom. The MCP client is now built once, for the endpoint and the chat.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

frontend/src/routes/_layout/settings.tsx

@@ -2,6 +2,7 @@ import { createFileRoute } from "@tanstack/react-router"
 import { motion } from "motion/react"
 
 import Appearance from "@/components/UserSettings/Appearance"
+import Assistant from "@/components/UserSettings/Assistant"
 import RemoteAccess from "@/components/UserSettings/RemoteAccess"
 import UserInformation from "@/components/UserSettings/UserInformation"
 import useAuth from "@/hooks/useAuth"
@@ -57,6 +58,12 @@ function UserSettings() {
             <RemoteAccess />
           </motion.div>
         )}
+        {/* One provider for everyone here, so the same rule applies. */}
+        {currentUser.is_superuser && (
+          <motion.div variants={slideUp}>
+            <Assistant />
+          </motion.div>
+        )}
       </motion.div>
     </div>
   )