Replicate the Plasma media plasmoid tray behavior on Linux SNI panels:
- Tooltip now shows live track title, "by Artist", album line, and
"Middle-click to play/pause" + "Scroll to adjust volume" hints.
- Middle-click (SecondaryActivate) emits tray:play_pause instead of
toggling the window — the window toggle stays on left-click.
- Mouse wheel (Scroll) emits tray:volume_delta with normalised ticks
(~120 SNI units per notch -> +/-5% volume per tick), wired to the
existing handleVolumeChange path on the frontend so QConnect remote
renderers and the local player both respond.
Architecture: ksni 0.3.4's blocking Handle is now stored as
LinuxTrayHandle in Tauri state. v2_set_media_metadata pushes track
fields into the tooltip, and the playback poll loop mirrors the
play/pause flag so the hint flips while the panel popup is open.
cc
vicrodh
789b0262b6