installDebugTokenFromLocalProperties

Local-development helper that seeds the deprecated TokenHolder shim with a token read from local.properties (spotify.token or SPOTIFY_TOKEN).

Best-effort by design: a missing or unreadable file and an absent key all leave the holder untouched instead of failing. The value is loaded once rather than registered as a provider, so a token installed later (for example by a completed authorization flow or a manual edit) always wins. Kept for manual JVM debugging only; production code should pass a TokenProvider (or access token) to SpotifyClient / the *Apis classes instead.