chat: rename the pi chat transport + model list to chat (Stage 4b/1)

Pure rename, no behavior change. Moves the misnamed "pi" chat harness into the
chat namespace:

- api/pi/{websocket,session-manager,types,logger,list-models} → api/chat/
- merge api/pi/rest.ts into api/chat/chat.ts (/pi/models → /chat/models,
  /pi/stt → /chat/stt); drop the piRestRouter mount
- PiEvent → ChatEvent, piWebsocket → chatWebsocket, listPiModels → listChatModels
- WS route /api/pi/chat/ws → /api/chat/ws, provider tag 'pi' → 'chat'
- frontend: useChat/useAudioRecording URLs, usePiModels→useModels /
  useVisiblePiModels→useVisibleModels / useEnabledPiModels→useEnabledModels,
  'PI_MODELS' query key → 'CHAT_MODELS', attachments provider 'pi-mono' → 'chat'

The /pi-mono provider/harness settings router is renamed separately (next commit).
Note: the WS route change requires the mobile app to point at /api/chat/ws.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/server.tsx

@@ -5,7 +5,7 @@ import { honoServer } from './servers/hono';
 import { verify } from './servers/jwt';
 import { isTokenBlacklisted } from 'officerdb';
 import { terminalWebsocket } from './servers/api/terminal/websocket';
-import { piWebsocket } from './servers/api/pi/websocket';
+import { chatWebsocket } from './servers/api/chat/websocket';
 import { taskRunnerWebsocket } from './servers/api/tasks/task-executor';
 import { pipelineWebsocket } from './servers/api/tasks/pipeline-executor';
 import { cliampWebsocket } from './servers/api/cliamp/websocket';
@@ -33,7 +33,7 @@ type WSData = {
   email: string;
   username: string;
   role: string;
-  provider: 'terminal' | 'pi' | 'task-runner' | 'pipeline' | 'dev-server' | 'cliamp' | 'cliamp-audio' | 'desktop' | 'sidecar';
+  provider: 'terminal' | 'chat' | 'task-runner' | 'pipeline' | 'dev-server' | 'cliamp' | 'cliamp-audio' | 'desktop' | 'sidecar';
   sandboxed: boolean;
   sessionId?: string;
   cwd?: string;
@@ -131,7 +131,7 @@ async function handleSidecarQueueCommand(ws: ServerWebSocket<WSData>, msg: Recor
 
 const handlers: Record<string, any> = {
   terminal: terminalWebsocket,
-  pi: piWebsocket,
+  chat: chatWebsocket,
   'task-runner': taskRunnerWebsocket,
   pipeline: pipelineWebsocket,
   cliamp: cliampWebsocket,
@@ -205,7 +205,7 @@ const devServerWebsocket = {
 };
 handlers['dev-server'] = devServerWebsocket;
 
-async function upgradeWs(req: Request, server: any, provider: 'terminal' | 'pi' | 'task-runner' | 'pipeline' | 'cliamp' | 'cliamp-audio' | 'desktop') {
+async function upgradeWs(req: Request, server: any, provider: 'terminal' | 'chat' | 'task-runner' | 'pipeline' | 'cliamp' | 'cliamp-audio' | 'desktop') {
   const token = new URL(req.url).searchParams.get('token');
   if (!token) return new Response('Unauthorized', { status: 401 });
 
@@ -292,7 +292,7 @@ const server = serve({
     '/api/tasks/run/ws': (req, server) => upgradeWs(req, server, 'task-runner'),
     '/api/tasks/pipeline/ws': (req, server) => upgradeWs(req, server, 'pipeline'),
     '/api/terminal/ws': (req, server) => upgradeWs(req, server, 'terminal'),
-    '/api/pi/chat/ws': (req, server) => upgradeWs(req, server, 'pi'),
+    '/api/chat/ws': (req, server) => upgradeWs(req, server, 'chat'),
     '/api/cliamp/ws': (req, server) => upgradeWs(req, server, 'cliamp'),
     '/api/cliamp/audio/ws': (req, server) => upgradeWs(req, server, 'cliamp-audio'),
     '/api/desktop/ws': (req, server) => upgradeWs(req, server, 'desktop'),