pi session context persistence, fix new session button, add clear all sessions

- handle pi process death by nulling piProcess ref so next message respawns
- replay conversation history on respawn via --session flag
- fix user message JSONL format to array for pi compatibility
- fix container sessions mount to match storage path
- fix ChatPanelWrapper: key on inner component so usePiChat resets on new session
- add bulk delete sessions endpoint and clear all button in chat header

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/servers/api/pi/rest.ts

@@ -235,6 +235,39 @@ piRestRouter.delete('/pi/sessions/:sessionId', async (ctx: Context) => {
   }
 });
 
+/**
+ * DELETE /api/pi/sessions
+ * Delete all sessions, optionally filtered by context
+ */
+piRestRouter.delete('/pi/sessions', async (ctx: Context) => {
+  const user = ctx.get('user');
+  if (!user) {
+    return ctx.json({ error: 'Unauthorized' }, 401);
+  }
+
+  const body = await ctx.req.json().catch(() => ({}));
+  const contextFilter = body.context ? { context: body.context as string, contextId: body.contextId as string | undefined } : undefined;
+  const userHome = getHomeDir(user.email);
+
+  try {
+    const sessions = await storage.listUserSessions(userHome, contextFilter);
+    let deleted = 0;
+    for (const session of sessions) {
+      try {
+        await storage.deleteSession(userHome, session.id, session.groupSlug);
+        deleted++;
+      } catch {
+        // Skip sessions that fail to delete
+      }
+    }
+    logger.info('Bulk deleted sessions', { email: user.email, deleted, total: sessions.length, context: contextFilter?.context });
+    return ctx.json({ success: true, deleted });
+  } catch (err) {
+    logger.error('Failed to bulk delete sessions', { email: user.email, error: String(err) });
+    return ctx.json({ error: 'Failed to delete sessions' }, 500);
+  }
+});
+
 /**
  * GET /api/pi/sessions/search
  * Search sessions by query