feat: migrate UID system from usernames to email addresses

- Database migration: Updated publicstream.uid from usernames to email addresses
  - devuser → oib@bubuit.net
  - oibchello → oib@chello.at
- Updated related tables (UploadLog, UserQuota) to use email-based UIDs
- Fixed backend audio route to map email UIDs to username-based directories
- Updated SSE event payloads to use email for UID and username for display
- Removed redundant display_name field from SSE events
- Fixed frontend rendering conflicts between nav.js and streams-ui.js
- Updated stream player template to display usernames instead of email addresses
- Added cache-busting parameters to force browser refresh
- Created migration script for future reference

Benefits:
- Eliminates UID duplicates and inconsistency
- Provides stable, unique email-based identifiers
- Maintains user-friendly username display
- Follows proper data normalization practices

Fixes: Stream UI now displays usernames (devuser, oibchello) instead of email addresses

list_streams.py

@@ -85,8 +85,7 @@ async def list_streams_sse(db):
                     'uid': stream.uid or '',
                     'size': stream.storage_bytes or 0,
                     'mtime': int(stream.mtime) if stream.mtime is not None else 0,
-                    'username': stream.username or stream.uid or '',
-                    'display_name': stream.display_name or stream.username or stream.uid or '',
+                    'username': stream.username or '',
                     'created_at': stream.created_at.isoformat() if stream.created_at else None,
                     'updated_at': stream.updated_at.isoformat() if stream.updated_at else None
                 }