V150: Readable device name on session tokens.

Adds nullable browser and os columns to phoenix_kit_users_tokens, parsed from the User-Agent at login (V43 already stores the hashed UA for fingerprint matching — the raw string, and thus the readable name, was never kept). Storing the parsed name lets the user's Active Sessions list and the admin all-sessions view show "Safari on iOS" for every session, independent of the new_login_alert_enabled setting (which gates the richer, more sensitive geo-location via known-devices).

Existing sessions predate the columns and show as "Unknown device" until their next sign-in — the raw UA was never stored, so there's nothing to backfill.