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/zh/settings.ts

@@ -200,6 +200,8 @@ export const settings = {
   preloadMiniPlayerDesc: '在应用启动时于后台构建迷你播放器窗口，使其首次打开即可立即显示内容。会占用少量额外内存。',
   linuxWebkitSmoothScroll: '滚轮平滑（Linux）',
   linuxWebkitSmoothScrollDesc: '开：惯性滚动。关：逐行，类似 GTK。',
+  linuxWebkitInputForceRepaint: '获得焦点时重绘输入框（Linux）',
+  linuxWebkitInputForceRepaintDesc: '针对 WebKitGTK 2.50.x 文本框点击后冻结的临时方案。聚焦时搜索图标会短暂闪烁。',
   linuxWaylandTextRender: 'Wayland 文本渲染（Linux）',
   linuxWaylandTextRenderDesc: '界面字体平滑立即生效。WebKit 硬件加速策略（锐利 / GPU）会保存并在下次启动应用时应用；运行中反复切换可能导致 WebKitGTK 卡死。',
   linuxWaylandTextRenderBalanced: '平衡',