Fix: missing typing-extensions dependency and handle missing API fields while using CLI

[imyimang]

1. Fix ModuleNotFoundError for typing-extensions

Added `typing-extensions` to the dependencies in `pyproject.toml`. This resolves a `ModuleNotFoundError` encountered when installing via `pipx` or in isolated environments where `Pylette`'s dependencies aren't fully propagated.

2. Fix KeyError: 'label' in spotify.py
   The application currently assumes that the Spotify API always returns a label field in the album metadata. However, when fetching tracks or certain simplified album objects, this field may be missing from the JSON response

{
    "album_type": "album",
    "total_tracks": 11,
    "external_urls": {
        "spotify": "https://open.spotify.com/album/3RBULTZJ97bvVzZLpxcB0j"
    },
    "id": "3RBULTZJ97bvVzZLpxcB0j",
    "images": [...],
    "name": "The Mountain",
    "release_date": "2013-09-17",
    "release_date_precision": "day",
    "type": "album",
    "uri": "spotify:album:3RBULTZJ97bvVzZLpxcB0j",
    "artists": [...],
    "tracks": {...},
    "copyrights": [...],
    "genres": []
    // No "label" field present
}

Changes:

• Replaced direct key access album["label"] with album.get("label", "") to provide a safe fallback.

After Fix:

3. Fix IndexError: list index out of range in write.py
   In write.py, the group_by_font function fails when it encounters characters that cannot be mapped to any predefined fonts (e.g., specific symbols or unidentifiable whitespace), resulting in an empty groups list. Attempting to access groups[0] without verification causes a crash.

Changes:

• Added a safety check to ensure groups is not empty before accessing its elements.

After Fix: