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/servers/api/chat/chat.ts

@@ -1,5 +1,6 @@
 import type { Context } from 'hono';
 import { createRouter } from '../../create-router';
+import { getUserSettings } from 'officerdb';
 import {
   getClaudeSessionsCwd,
   listClaudePwds,
@@ -8,6 +9,10 @@ import {
   deleteClaudeSession,
   renameClaudeSession,
 } from './claude-sessions';
+import { listChatModels } from './list-models';
+import { logger } from './logger';
+import { readSttConfig } from '../server-settings/stt';
+import { transcribeAudio } from '../stt/transcribe';
 
 export const chatRouter = createRouter();
 
@@ -52,3 +57,41 @@ chatRouter.patch('/sessions/:id/title', async (ctx) => {
   if (!ok) return ctx.text('Not found', 404);
   return ctx.json({ ok: true });
 });
+
+// GET /chat/models — Claude tiers only (the runner is the `claude` CLI).
+chatRouter.get('/models', async (ctx: Context) => {
+  try {
+    const models = await listChatModels();
+    const providerNames: Record<string, string> = { 'claude-code': 'Claude Code' };
+    return ctx.json({ models, providerNames, hostHome: process.env.HOME ?? '' });
+  } catch (err) {
+    logger.error('Failed to list models', { error: String(err) });
+    return ctx.json({ models: [], providerNames: {} });
+  }
+});
+
+// POST /chat/stt — proxy an audio clip to the configured Whisper server.
+chatRouter.post('/stt', async (ctx: Context) => {
+  const sttConfig = await readSttConfig();
+  if (!sttConfig?.url) {
+    return ctx.json({ error: 'Whisper not configured — set it up in Settings → Speech to Text' }, 400);
+  }
+
+  const user = ctx.get('user');
+  const body = await ctx.req.parseBody();
+  const file = body['file'];
+  if (!file || !(file instanceof File)) {
+    return ctx.json({ error: 'file is required' }, 400);
+  }
+
+  const settings = (await getUserSettings(user.id)) as { languages?: { spoken?: string[] } };
+  const spokenLanguages = settings.languages?.spoken ?? [];
+
+  try {
+    const result = await transcribeAudio({ file, whisperUrl: sttConfig.url, spokenLanguages });
+    return ctx.json(result);
+  } catch (err) {
+    logger.error('STT proxy failed', { error: String(err) });
+    return ctx.json({ error: err instanceof Error ? err.message : 'Failed to reach Whisper server' }, 502);
+  }
+});