feat(input): opt-in WebKitGTK focus repaint workaround for Linux (#342, #782) (#884)

* feat(input): opt-in WebKitGTK focus repaint workaround for Linux (#342, #782)

Some Linux users on WebKitGTK 2.50.x report a freeze when clicking
text fields: the field receives focus (right-click paste still works)
but the canvas never redraws until the window is resized. Likely a
layer-flush / composition scheduling bug in 2.50.x's Skia rendering
pipeline.

Off by default. When enabled in Settings -> System -> Behavior, every
input/textarea focus triggers a sync reflow read plus a one-frame
translateZ(0) toggle on the input's parent so WebKit re-evaluates the
layer tree. Side-effect: search-icon siblings flicker briefly on
focus -- accepted trade-off, only paid by users who opt in.

The toggle row is gated on IS_LINUX and sits next to the existing
Linux WebKitGTK options. The effect subscribes to the auth store and
re-attaches the focusin handler whenever the flag flips, so toggling
off cleanly removes the listener.

* i18n(settings): linux input repaint toggle in all locales

Adds linuxWebkitInputForceRepaint label + description across en, de,
fr, es, nl, nb, ro, zh, ru.

* docs(release): CHANGELOG and credits for linux input freeze workaround (PR #884)

src/config/settingsCredits.ts

@@ -336,6 +336,7 @@ const CONTRIBUTOR_ENTRIES = [
       'Interface Scale: scales the entire window — sidebar, queue, player bar, modals and the fullscreen player follow the main content (PR #781)',
       'Local library index (preview): SQLite per-server track store, background initial and delta sync, live and Advanced Search against the local index, integrity verify and auto-reconcile on count drop (PR #846)',
       'Server index-key rebuild: safe dual-DB migration flow, per-server analysis strategy controls, and playback/index scope hardening (PR #864)',
+      'Settings: opt-in Linux input-focus repaint — workaround for the WebKitGTK 2.50.x text-field freeze (PR #884)',
     ],
   },
 ] as const;