improve startup logging: version, platform, data dir, db stats

Replace verbose startup messages with a clean summary:
- App version, Python version, OS/arch
- Database path (fix None display), data directory
- Profile and generation counts
- Backend, GPU, model cache path
- Clean up stale loading_model status on startup
- Remove noisy progress manager log line

backend/utils/cache.py

@@ -3,12 +3,15 @@ Voice prompt caching utilities.
 """
 
 import hashlib
+import logging
 import torch
 from pathlib import Path
 from typing import Optional, Union, Dict, Any
 
 from .. import config
 
+logger = logging.getLogger(__name__)
+
 
 def _get_cache_dir() -> Path:
     """Get cache directory from config."""
@@ -93,17 +96,17 @@ def cache_voice_prompt(
 def clear_voice_prompt_cache() -> int:
     """
     Clear all voice prompt caches (memory and disk).
-    
+
     Returns:
         Number of cache files deleted
     """
     # Clear memory cache
     _memory_cache.clear()
-    
+
     # Clear disk cache
     cache_dir = _get_cache_dir()
     deleted_count = 0
-    
+
     if cache_dir.exists():
         # Delete prompt cache files
         for cache_file in cache_dir.glob("*.prompt"):
@@ -111,32 +114,32 @@ def clear_voice_prompt_cache() -> int:
                 cache_file.unlink()
                 deleted_count += 1
             except Exception as e:
-                print(f"Failed to delete cache file {cache_file}: {e}")
-        
+                logger.warning("Failed to delete cache file %s: %s", cache_file, e)
+
         # Delete combined audio files
         for audio_file in cache_dir.glob("combined_*.wav"):
             try:
                 audio_file.unlink()
                 deleted_count += 1
             except Exception as e:
-                print(f"Failed to delete combined audio file {audio_file}: {e}")
-    
+                logger.warning("Failed to delete combined audio file %s: %s", audio_file, e)
+
     return deleted_count
 
 
 def clear_profile_cache(profile_id: str) -> int:
     """
     Clear cache files for a specific profile.
-    
+
     Args:
         profile_id: Profile ID
-    
+
     Returns:
         Number of cache files deleted
     """
     cache_dir = _get_cache_dir()
     deleted_count = 0
-    
+
     if cache_dir.exists():
         # Delete combined audio files for this profile
         pattern = f"combined_{profile_id}_*.wav"
@@ -145,6 +148,6 @@ def clear_profile_cache(profile_id: str) -> int:
                 audio_file.unlink()
                 deleted_count += 1
             except Exception as e:
-                print(f"Failed to delete combined audio file {audio_file}: {e}")
-    
+                logger.warning("Failed to delete combined audio file %s: %s", audio_file, e)
+
     return deleted_count