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/swarm.py

@@ -21,6 +21,7 @@ orphans 同款口径），下次成功保存即覆盖自愈。
 from __future__ import annotations
 
 import json
+import sqlite3
 import logging
 import os
 import time
@@ -79,7 +80,7 @@ def _load_registry(state_dir: str) -> dict:
     try:
         with _open_store(state_dir) as store:
             raw = store.kv_get(_KV_NAMESPACE, _KV_KEY)
-    except Exception:
+    except (sqlite3.Error, OSError):
         _LOGGER.warning("chv_swarm_registry_store_unreadable "
                         "state_dir=%s", state_dir)
         return _empty_registry()
@@ -128,7 +129,7 @@ def _import_legacy(state_dir: str) -> dict:
     try:
         with _open_store(state_dir) as store:
             store.kv_put(_KV_NAMESPACE, _KV_KEY, json.dumps(data))
-    except Exception:
+    except (sqlite3.Error, OSError):
         _LOGGER.warning("chv_swarm_registry_import_failed "
                         "state_dir=%s", state_dir)
         return data
@@ -148,7 +149,7 @@ def _save_registry(state_dir: str, data: dict) -> None:
     try:
         with _open_store(state_dir) as store:
             store.kv_put(_KV_NAMESPACE, _KV_KEY, json.dumps(data))
-    except Exception:
+    except (sqlite3.Error, OSError):
         _LOGGER.warning("chv_swarm_registry_save_failed "
                         "state_dir=%s", state_dir)