Add explicit encoding="utf-8" to all config/data file open() calls

On Windows, open() defaults to the system locale encoding (cp1252,
cp1254, etc.) rather than UTF-8. This breaks any file containing
non-ASCII characters, and also causes crashes when writing JSON with
ensure_ascii=False.

This adds encoding="utf-8" to open() calls in:
- gateway/run.py (config.yaml reads/writes throughout)
- gateway/config.py (gateway.json and config.yaml)
- hermes_cli/config.py (config.yaml load/save)
- hermes_cli/main.py (session export with ensure_ascii=False)
- hermes_cli/status.py (jobs.json and sessions.json)

hermes_cli/main.py

@@ -1549,12 +1549,12 @@ For more help on a command:
                 if not data:
                     print(f"Session '{args.session_id}' not found.")
                     return
-                with open(args.output, "w") as f:
+                with open(args.output, "w", encoding="utf-8") as f:
                     f.write(_json.dumps(data, ensure_ascii=False) + "\n")
                 print(f"Exported 1 session to {args.output}")
             else:
                 sessions = db.export_all(source=args.source)
-                with open(args.output, "w") as f:
+                with open(args.output, "w", encoding="utf-8") as f:
                     for s in sessions:
                         f.write(_json.dumps(s, ensure_ascii=False) + "\n")
                 print(f"Exported {len(sessions)} sessions to {args.output}")