[Linuxuser67]

Best match (combo index 0) carried the global Preferred quality instead of best available, so x.com Best-match rows downloaded at the preference height while manual picks landed correctly.

• Index 0 now stores quality best (tallest split / muxed / HLS variant in every path — all arms already handle it).
• The global preference keeps its job as the preselected combo row at resolve time (new pure default_quality_index: Best stays on Best match, else closest listed height, ties taller).
• Exact picks unchanged (pin + picked height).

218 passing, clippy clean. No string changes (label already says Best match, truthfully now).