jellytoast v0.1.2

A correctness-and-hardening release from a full release-readiness review of the
app: the Linux .deb now launches on X11/XWayland, plus a Jellyfin
playback/launch crash, a fresh-install credential-permission leak, and a set of
cast, offline, and UI fixes.

Fixed

• The Linux .deb now launches on X11 / XWayland. The bundled Qt xcb
  platform plugin hard-links a large X / xcb / xkb / font / GL library closure
  that the package only partially declared, so on a minimal install an X11 (or
  XWayland) session aborted at startup ("could not load the Qt platform plugin
  xcb"). The package now Depends on the complete closure, proven by a clean-
  container boot across Ubuntu 24.04 / 26.04 and Debian stable. v0.1.0 and
  v0.1.1's .deb were affected too; Wayland sessions were never affected.
• Jellyfin tracks with an unknown duration no longer crash playback — or
  launch. Jellyfin reports RunTimeTicks / UserData as present but null
  for un-probed, .strm, and some live items; the now-playing builder treated
  only an absent field as missing, so such a track raised a TypeError when
  played or prefetched, and — if it was the saved resume track — aborted startup
  before the window appeared. Subsonic / Navidrome were unaffected.
• Downloads no longer follow you across a sign-out or server switch.
  In-flight and queued downloads planned against the previous server are now
  cancelled on sign-out / server change, so they can't land in the next
  account's offline library.
• Internet radio casts reliably to DLNA and Sonos. Live / ICY radio streams
  are now handed to the speaker directly instead of through the local cast relay
  (matching the Chromecast path), which could stall an endless stream.
• Legacy AirPlay no longer leaks a connection when a receiver drops
  mid-request.
• Less spurious offline flicker on a slow failover — the connectivity check
  re-confirms its timing window, not just the failure count, before switching to
  offline mode.
• Keyboard navigation in Search no longer makes the next mouse-wheel scroll
  jump back. Programmatic scrolls now reset the smooth-scroll state.

Security

• The credential file is owner-only from the very first launch. The config
  file — which holds the encrypted token plus your username and server address —
  was briefly created world-readable on a fresh Linux install and only tightened
  to 0600 on the next launch; it is now tightened the moment it is first
  written. (No effect on Windows, which stores credentials in the OS credential
  manager.)

Performance

• Large libraries build their A–Z index faster — a per-row sort-field lookup
  that is constant across a load is now computed once instead of per item.