feat: complete timezone support for NFO dateadded fields

- Fix NFO dateadded timestamps to use local timezone instead of UTC
- Convert Radarr/Sonarr import dates from UTC to local timezone for NFO files
- Update webhook episode processing to use local time for new downloads
- Convert file modification time fallbacks to local timezone
- Preserve historical dates (aired, premiered) in original UTC format
- Replace all placeholder logging functions with centralized timezone-aware logging
- Add convert_utc_to_local() utility function for timestamp conversion
- Now all logs AND NFO files show consistent local timezone formatting

Users with TZ=America/New_York will now see:
- Logs: [2025-09-14T09:37:00-04:00]
- NFO files: <dateadded>2025-09-14T09:37:00-04:00</dateadded>

core/logging.py

@@ -26,4 +26,28 @@ def _get_local_timezone():
 def _log(level: str, msg: str):
     """Basic logging function that writes to console"""
     tz = _get_local_timezone()
-    print(f"[{datetime.now(tz).isoformat(timespec='seconds')}] {level}: {msg}")
+    print(f"[{datetime.now(tz).isoformat(timespec='seconds')}] {level}: {msg}")
+
+def convert_utc_to_local(utc_iso_string: str) -> str:
+    """Convert UTC ISO timestamp to local timezone timestamp"""
+    if not utc_iso_string:
+        return utc_iso_string
+    
+    try:
+        # Parse UTC timestamp
+        if utc_iso_string.endswith('Z'):
+            dt_utc = datetime.fromisoformat(utc_iso_string.replace('Z', '+00:00'))
+        elif '+00:00' in utc_iso_string:
+            dt_utc = datetime.fromisoformat(utc_iso_string)
+        else:
+            # Assume UTC if no timezone info
+            dt_utc = datetime.fromisoformat(utc_iso_string).replace(tzinfo=timezone.utc)
+        
+        # Convert to local timezone
+        local_tz = _get_local_timezone()
+        dt_local = dt_utc.astimezone(local_tz)
+        
+        return dt_local.isoformat(timespec='seconds')
+    except Exception:
+        # If conversion fails, return original
+        return utc_iso_string