fix(integration): sessions CLI — close db via try/finally, complete test doubles

cmd_sessions used 'with db:' which breaks test doubles lacking the context
manager protocol (13 reds in test_sessions_pin/delete/export). Restore the
explicit try/finally db.close() (same semantics for real SessionDB). Add
get_session/count_prune_matches to the FakeDB doubles in test_sessions_delete
instead of re-adding getattr guards to production code.

hermes_cli/sessions_cmd.py

@@ -950,9 +950,11 @@ def cmd_sessions(args, sessions_parser=None):
     except Exception as e:
         print(f"Error: Could not open session database: {e}")
         return 1
-    with db:
+    try:
         handler = _DB_HANDLERS.get(action)
         if handler is None:
             sessions_parser.print_help()
             return
         return handler(db, args)
+    finally:
+        db.close()

tests/hermes_cli/test_sessions_delete.py

@@ -14,6 +14,9 @@ def test_sessions_delete_accepts_unique_id_prefix(monkeypatch, capsys):
             captured["resolved_from"] = session_id
             return "20260315_092437_c9a6ff"
 
+        def get_session(self, session_id):
+            return {"id": session_id, "pinned": 0}
+
         def delete_session(self, session_id, **kwargs):
             captured["deleted"] = session_id
             return True
@@ -78,6 +81,9 @@ def _run_prune(monkeypatch, capsys, argv_tail, candidates=None, skipped_open=0):
             assert kwargs == seen
             return skipped_open
 
+        def count_prune_matches(self, **kwargs):
+            return len(rows)
+
         def prune_sessions(self, **kwargs):
             return len(rows)