radoslav-orlov: add AAC as a download quality option. AAC is more efficient than
MP3, so it's useful for Soulseek/torrents (streaming sources pick their own
codec; Amazon — the AAC-heavy one — is down).
Additive by construction: every quality tier already defaults enabled=false and
the waterfall is built only from enabled tiers, so AAC ships OFF and the bucketer
routes a not-enabled AAC file to the 'other' bucket EXACTLY as today (where it was
silently dropped). Only a user who turns AAC on makes it a first-class tier,
ranked above MP3 / below FLAC (priority 1.5, min-kbps gate so junk AAC can't beat
a good MP3).
- music_database: aac tier (disabled) in the default profile + all 3 presets.
- soulseek_client: map .m4a -> 'aac' in both result parsers (was 'unknown' ->
dropped); add the 'aac' bucket + a gated branch + a fallback size limit.
- settings UI: an 'AAC' tier toggle (unchecked) between FLAC and MP3; save
defaults its priority to 1.5 so upgraded profiles rank it right on first save.
7 seam tests pinning the additive guarantee (aac absent/disabled -> dropped as
before; FLAC/MP3 selection unchanged; aac on -> selectable, below FLAC, above
MP3); 81 quality/soulseek tests pass, ruff clean. quality_upgrade left untouched
(its AAC handling is unchanged).
400b35d655