round-12: ruff hygiene on migration code (import sort, narrow store except)

- test_chv_muse_round12.py: drop unused socket/time imports, drop
  unnecessary sys.path.insert (P3 pattern needs none), sort method-local
  imports (activity/capabilities, approval_card/channel/sentinel)
- audit_trail.py: single-line method-local imports (I001)
- swarm.py / presentation.py / browser_tasks.py: store-path fail-safe
  except narrowed from bare Exception to (sqlite3.Error, OSError)
  (DB/file failures only); transport spawn/ping/close handlers in
  browser_tasks.py deliberately stay bare Exception (arbitrary
  transport errors must map to failed/False/close_error)
- NOT fixed (pre-existing style, left as-is): UP031 % formatting
  (used throughout the codebase incl. the copied lines), BLE001/
  TRY004 in untouched code, F401 atomic_write + RUF059 swarm
  (P7/P8 pre-existing)

cloud/chv/audit_trail.py

@@ -338,8 +338,7 @@ class StoreAuditTrail:
 
     def _open_store(self):
         """打开宿主级状态库（每次调用新建连接，用完即关）。"""
-        from cloud.chv.app_state import AppStateStore, \
-            host_state_db_path
+        from cloud.chv.app_state import AppStateStore, host_state_db_path
         store = AppStateStore(host_state_db_path(self.state_dir))
         store.open()
         return store
@@ -453,8 +452,7 @@ def migrate_jsonl_to_store(path: str, state_dir: str) -> int:
         raise ValueError("JSONL 审计链校验失败，拒绝迁移：行 %d"
                          % bad)
     rows = trail._read_all()
-    from cloud.chv.app_state import AppStateStore, \
-        host_state_db_path
+    from cloud.chv.app_state import AppStateStore, host_state_db_path
     store = AppStateStore(host_state_db_path(state_dir))
     store.open()
     try: