Update token cache and repair environment setup

[simra]

This pull request updates the weekly-catalog-update GitHub Actions workflow to improve environment variable management and add a step for pre-seeding the Spotify token cache. The changes focus on enhancing security and reliability by using repository/environment variables instead of secrets for non-sensitive data, and by ensuring the Spotify authentication cache is properly initialized before running the catalog processing script.

Workflow improvements:

• Added an environment key to the update-catalog job to specify the deployment environment as "weekly update".

Environment variable management:

• Updated environment variable sourcing: switched from using secrets to vars for non-sensitive configuration values such as SPOTIPY_REDIRECT_URI, SPOTIFY_USERNAME, PLAYLIST_NAME, DAYS_TO_PARSE, TOP_N, and PIVOT. Sensitive values like SPOTIPY_CLIENT_ID, SPOTIPY_CLIENT_SECRET, and SPOTIFY_REFRESH_TOKEN remain in secrets.

Spotify authentication handling:

• Added a new step to pre-seed the Spotify token cache file (.cache-${SPOTIFY_USERNAME}) with a placeholder access token and the actual refresh token from secrets, ensuring the subsequent catalog processing script can authenticate with Spotify.