features: add commit and push option to git commit window

- Add split button with dropdown in commit dialog supporting both
  "Commit" and "Commit and Push" actions
- Pass folderId through gitCommit/gitPush API calls so backend emits
  events that the folder window can receive for toast notifications
- Update Tauri git_commit and git_push commands to accept folder_id
  parameter with window label fallback for cross-window compatibility
- Wrap commit page with GitCredentialProvider for push authentication
- Keep commit window open when push fails so user can see the error
- Add i18n translations for all 10 locales

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/i18n/messages/de.json

@@ -1009,6 +1009,7 @@
     "commitDialog": {
       "toasts": {
         "commitCompleted": "Code-Commit abgeschlossen",
+        "pushFailed": "Push fehlgeschlagen",
         "committedFiles": "{count, plural, one {# Datei committet} other {# Dateien committet}}",
         "addedToVcs": "Zu VCS hinzugefügt",
         "addToVcsFailed": "Hinzufügen zu VCS fehlgeschlagen",
@@ -1050,6 +1051,7 @@
       "commitMessage": "Commit-Nachricht",
       "commitMessagePlaceholder": "Commit-Nachricht eingeben...",
       "commitButton": "Einchecken ({count})",
+      "commitAndPushButton": "Committen und pushen ({count})",
       "head": "HEAD",
       "workingTree": "Arbeitsverzeichnis",
       "clickFileToDiff": "Dateinamen anklicken, um Diff zu sehen",