feat(ui): show the changed-files count badge on the Git rail surface

Replaces the plain activity dot on the context panel rail's Git button with
a numeric badge of the changed-files count from the git store status, so the
count is visible at a glance without opening the Git surface. Large counts
cap at 99+ to keep the pill within the 36px button. The badge is reflected
in the button's accessible label and the hover tooltip.

Fixes #2364

packages/ui/src/lib/i18n/messages/es.ts

@@ -1107,6 +1107,8 @@ export const dict: Record<I18nKey, string> = {
   "contextPanel.editorEmpty.description": "Elige un archivo del árbol para empezar a editar.",
   "contextRail.surface.editor.description": "Editar archivos del proyecto",
   "contextRail.surface.git.description": "Commits, ramas y pull requests",
+  "contextRail.surface.git.changesCountAria": "{label}, {count} archivos modificados",
+  "contextRail.surface.git.changesCountTooltip": "{count} archivos modificados",
   "contextRail.surface.terminal.description": "Terminal integrada",
   "contextRail.surface.diff.description": "Revisar cambios en curso",
   "contextPanel.mode.walkthrough": "Recorrido",