fix(update): make the release notes in the update dialog scrollable

[ReichiMD]

Summary

The release notes in the app update dialog could not be scrolled — not by swiping on touch devices, not with the D-pad on TV. They were cut at 900 characters and 260 dp, while the actual release notes are 3–15 KB, so most of the text was never reachable. Both places that open the dialog (automatic check on Home, Settings → check for updates) share AppUpdateModal, so both are fixed.

Changes (only AppUpdateModal.kt + one unit test)

• Only the notes area scrolls (verticalScroll); title and buttons stay fixed. The notes take weight(1f, fill = false) with the existing 260 dp cap, so on short or landscape screens they give up height first and the buttons stay on screen.
• TV: D-pad up/down scrolls the notes. The key is consumed only while the notes can still move in that direction; at the edges it falls through exactly as before. Left/right/OK are unchanged. A held key scrolls without restarting the animation.
• A short fade on the top/bottom edge shows that the text continues.
• The button row is a FlowRow: on narrow phones (e.g. German labels on a 360 dp screen) it wraps instead of squeezing the primary "Download" button. On TV (760 dp) it stays one row.
• The 900-character cut is replaced by a 20,000-character guard against a runaway release body.
• A small vertical margin keeps the dialog off the screen edges; tapping outside still dismisses it.

Not in this PR — happy to do it if you want

The notes are the raw GitHub release body, so ##, ** and links show as plain text — now the whole text, including the link lines at the end (and the Obtainium badge <img> from the release template). A light plain-text cleanup (drop heading/emphasis markers, turn [text](url) into text, drop images) or stopping at the "Downloads"/"Get ARVIO" section would be a small follow-up. I kept it out to keep this PR minimal.

Testing

• Unit test AppUpdateNotesScrollTest (D-pad step, edges, short notes never consume up/down).
• Device test (sideload debug build with a lowered versionName so the dialog appears):
  • Tablet, touch layout: dialog opens on its own after start, notes scroll to the very end by swiping, buttons stay visible throughout.
  • Phone in landscape: buttons stay on screen.
  • Phone in TV layout with a D-pad remote: up/down scrolls the notes, left/right moves between buttons.
  • Settings → check for updates: same dialog, same behaviour.

created by Claude (Anthropic) on behalf of @ReichiMD

[ProdigyV21]

Useful focused improvement: release notes can be scrolled without pushing the action buttons away, and buttons wrap on narrow screens. Reviewed the layout and D-pad handling; scroll-boundary unit tests pass and both Android variants compile. Integrated with current main and preserving your original commits.