chat: retire the old saved-session store (Stage 4a)

Deletes all session persistence that isn't Claude's native transcript store, per
the "only harness-native session management survives" rule.

Backend: delete api/pi/storage.ts (meta.json+messages.json file store), the
api/saved-sessions router (+ unmount), the /pi/sessions REST endpoints, and the
storage.save/loadSession calls in the chat WS handler (in-memory session-manager
stays for live turns; no disk persistence — Claude's transcript is the record).
Also drops the Postgres saved_sessions layer: schema/chat.ts, queries/saved-sessions.ts,
its types and re-exports.

Frontend: delete state/useSavedSessions, ChatList, and the ChatHistory Widget
(all pure saved-session UI); slim ChatHeader to a label; strip the auto-load-latest
+ Save wiring from ChatPanelWrapper and ChatDetailPanel; drop the old resume path
from useChat and SessionListPage; remove the /chat/saved/:id route and the
useInitialData prefetch.

Behavior removed (intended): the Save-session button, email/project panels
auto-resuming the last chat, and /chat/saved/:id. /chat itself is unchanged —
already fully on Claude transcripts. The orphaned saved_sessions Postgres table
is dropped on the next `bun db:push`.

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

src/servers/api/pi/rest.ts

@@ -1,9 +1,7 @@
 import type { Context } from 'hono';
 import { createRouter } from '../../create-router';
-import * as storage from './storage';
 import { readSttConfig } from '../server-settings/stt';
 import { listPiModels } from './list-models';
-import { getHomeDirForRole } from '../../data-path';
 import { logger } from './logger';
 import { transcribeAudio } from '../stt/transcribe';
 import { getUserSettings } from 'officerdb';
@@ -24,31 +22,6 @@ piRestRouter.get('/pi/models', async (ctx: Context) => {
   }
 });
 
-/**
- * GET /api/pi/sessions/:sessionId
- * Get session detail with full message history (used by active chat to load messages)
- */
-piRestRouter.get('/pi/sessions/:sessionId', async (ctx: Context) => {
-  const user = ctx.get('user');
-  if (!user) {
-    return ctx.json({ error: 'Unauthorized' }, 401);
-  }
-
-  const sessionId = ctx.req.param('sessionId');
-  if (!sessionId) {
-    return ctx.json({ error: 'Session ID required' }, 400);
-  }
-
-  const userHome = getHomeDirForRole(user.email, user.role);
-
-  try {
-    const { meta, messages } = await storage.loadSession(userHome, sessionId);
-    return ctx.json({ session: { ...meta, messages } });
-  } catch {
-    return ctx.json({ error: 'Session not found' }, 404);
-  }
-});
-
 /**
  * POST /api/pi/stt
  */