fix(player): make the video seek bar work by touch (DR-099)

On Android, dragging or tapping the progress bar moved the thumb but
playback stayed where it was. Two separate defects, both touch-only,
which is why the mouse-driven scrub tests never caught either.

1. Gesture hijack. DR-098 taught handleTouchStart to ignore touches that
   land on a control, but handleTouchMove kept running. It measures
   against touchStartX/Y, which that early return leaves at the PREVIOUS
   gesture's values, so a seek-bar drag produced a huge bogus vertical
   delta: read as a brightness swipe, it dimmed the screen to the 0.3
   floor and fired a spurious play/pause "correction" mid-drag. A gesture
   is now latched at touchstart (playerGestureActive) and touchmove
   ignores anything unlatched — re-checking the move target cannot
   recover a start point that was never recorded.

2. Commit signal. The seek was committed only from `change`, which
   Android's WebView does not reliably fire for a touch interaction on a
   range input, so the thumb moved to the tapped position and no seek
   ever ran. touchend/mouseup now commit too; `input` arms a one-shot
   latch so whichever release signal arrives first commits and the other
   is a no-op. seekRelative shares the same commitSeek entry point
   instead of fabricating a synthetic change event.

Tests drive the slider with real touch events (UT-089, UT-090) and fail
against the pre-fix component.

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "jellytau"
-version = "0.2.7"
+version = "0.2.8"
 description = "A Tauri App"
 authors = ["you"]
 edition = "2021"