When using long model names (e.g. OpenRouter models like
'openai/whisper-large-v3-turbo'), the combo boxes in Settings were
too narrow to display them, showing truncated text like 'open...ribe'.
Apply QSizePolicy.Expanding (horizontal) to all editable QComboBoxes
so they stretch to fill the available width of the form layout, just
as non-editable selects already do.
Affected boxes: transcribe_model, cleanup_model, cleanup_claude_model,
cleanup_codex_model, assistant_model, assistant_codex_model,
assistant_openrouter_model, meeting_model, paste_shortcut, repo,
and all shortcut picker boxes.
