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/components/Sidebar/AppSidebar.tsx

@@ -1,7 +1,9 @@
+import { useQuery } from "@tanstack/react-query"
 import {
   ArrowLeft,
   Bell,
   BookOpen,
+  Bot,
   FlaskConical,
   Home,
   KeyRound,
@@ -16,6 +18,8 @@ import {
 } from "lucide-react"
 import { useState } from "react"
 
+import { aiStatusQueryOptions, ChatPanel } from "@/components/Chat/ChatPanel"
+import { chatStore } from "@/components/Chat/chatStore"
 import { GlobalSearch } from "@/components/Common/GlobalSearch"
 import { Logo } from "@/components/Common/Logo"
 import {
@@ -97,10 +101,17 @@ export function AppSidebar() {
     onClick: () => setSearchOpen(true),
   }
 
+  // Only once an operator has set a provider up: with none there is nothing
+  // to open, and nothing on screen says the feature exists.
+  const assistant = useQuery(aiStatusQueryOptions())
+  const tools: Item[] = assistant.data?.available
+    ? [{ icon: Bot, title: "Assistant", onClick: chatStore.toggle }, search]
+    : [search]
+
   const footerItems: Item[] = portal
-    ? [search, docs, { icon: Settings, title: "Settings", path: "/settings" }]
+    ? [...tools, docs, { icon: Settings, title: "Settings", path: "/settings" }]
     : [
-        search,
+        ...tools,
         docs,
         { icon: Settings, title: "Settings", path: "/settings" },
         { icon: LogOut, title: "Log Out", onClick: logout },
@@ -140,6 +151,10 @@ export function AppSidebar() {
       {/* Outside the sidebar: on a phone that is a sheet, and a dialog is not
           one of its children. */}
       <GlobalSearch open={searchOpen} onOpenChange={setSearchOpen} />
+      {/* Mounted once, here, for the same reason: both shells carry the
+          sidebar, and the chat follows whoever opened it from screen to
+          screen. */}
+      <ChatPanel />
     </>
   )
 }