fix: preserve user-added voice fields across container restarts

generate_voices.py previously overwrote voices.json completely on every
start, discarding any manually added temperature/top_k/top_p fields.
Now loads existing voices.json first and merges user-added fields into
freshly generated entries, so per-voice sampling params survive restarts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/generate_voices.py

@@ -20,6 +20,16 @@ SCAN_DIRS = [
     "/voices",
 ]
 
+# Load existing voices.json so manually added fields (temperature, top_k,
+# top_p, chunk_size overrides, etc.) survive a container restart.
+_existing = {}
+if os.path.exists(output_file):
+    try:
+        with open(output_file, encoding="utf-8") as _f:
+            _existing = json.load(_f)
+    except (json.JSONDecodeError, OSError):
+        pass
+
 voices = {}
 
 
@@ -95,6 +105,13 @@ for scan_dir in SCAN_DIRS:
                 with open(txt, encoding="utf-8") as f:
                     entry["ref_text"] = f.read().strip()
 
+            # Preserve any user-added fields from the previous voices.json
+            # (temperature, top_k, top_p, chunk_size overrides, etc.)
+            if voice_id in _existing:
+                for key, val in _existing[voice_id].items():
+                    if key not in entry:
+                        entry[key] = val
+
             voices[voice_id] = entry
 
 with open(output_file, "w", encoding="utf-8") as f: