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/status.py

@@ -232,7 +232,7 @@ def show_status(args):
     if jobs_file.exists():
         import json
         try:
-            with open(jobs_file) as f:
+            with open(jobs_file, encoding="utf-8") as f:
                 data = json.load(f)
                 jobs = data.get("jobs", [])
                 enabled_jobs = [j for j in jobs if j.get("enabled", True)]
@@ -252,7 +252,7 @@ def show_status(args):
     if sessions_file.exists():
         import json
         try:
-            with open(sessions_file) as f:
+            with open(sessions_file, encoding="utf-8") as f:
                 data = json.load(f)
                 print(f"  Active:       {len(data)} session(s)")
         except Exception: