fix: 修复19个Bug (P0-P3) — 持续性调试第7轮发现的问题

P0 (5): crypto/rand session ID, TTS fallback可达性, goroutine defer recover, adminAuth前缀修正
P1 (5): 普通用户密码验证, context传递, priority clamp, 超时重试, 自主思考速率限制
P2 (4): Briefing AI降级, 前端消息类型渲染, Docker Compose补全, PWA 192图标
P3 (5): goroutine错误处理, .gitignore完善, reminder created_at, voice Dockerfile, Go版本更新

backend/ai-core/internal/subsession/manager.go

@@ -89,6 +89,11 @@ func (m *Manager) Dispatch(
 		wg.Add(1)
 		go func(p Provider) {
 			defer wg.Done()
+			defer func() {
+				if r := recover(); r != nil {
+					log.Printf("[subsession] dispatch goroutine panic 恢复 (type=%s): %v", p.Type(), r)
+				}
+			}()
 
 			result := model.SubSessionResult{Type: p.Type()}
 
@@ -135,6 +140,11 @@ func (m *Manager) Dispatch(
 
 	// 等待所有子会话完成，关闭通道
 	go func() {
+		defer func() {
+			if r := recover(); r != nil {
+				log.Printf("[subsession] wait goroutine panic 恢复: %v", r)
+			}
+		}()
 		wg.Wait()
 		close(resultCh)
 	}()