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/locales/nb/settings.ts

@@ -199,6 +199,8 @@ export const settings = {
   preloadMiniPlayerDesc: 'Bygger miniavspiller-vinduet i bakgrunnen ved appstart slik at det viser innhold umiddelbart ved første åpning. Bruker litt mer minne.',
   linuxWebkitSmoothScroll: 'Mykt musehjul (Linux)',
   linuxWebkitSmoothScrollDesc: 'På: treg rull med etterslep. Av: trinnvis som i GTK.',
+  linuxWebkitInputForceRepaint: 'Tegne om tekstfelt ved fokus (Linux)',
+  linuxWebkitInputForceRepaintDesc: 'Omgår WebKitGTK 2.50.x der tekstfelt fryser ved klikk. Søkeikoner blinker kort ved fokus.',
   linuxWaylandTextRender: 'Wayland-tekstgjengivelse (Linux)',
   linuxWaylandTextRenderDesc:
     'Utjevning i grensesnittet skjer med én gang. WebKit-maskinvareakselerasjon (skarp/GPU) lagres og brukes ved neste appstart — live bytte kan fryse WebKitGTK.',