feat: update user-facing 'Simple Mode' terminology to 'App Mode' (#8590)

## Summary
Updates all user-facing instances of 'Simple Mode' / 'Linear Mode' to
'App Mode' as discussed in PR #8562.

## Changes
- Updated command label in `useCoreCommands.ts`
- Updated `src/locales/en/commands.json`
- Updated all 12 locale `main.json` files with:
  - `linearMode.linearMode` → "App Mode" (translated)
  - `linearMode.beta` → "App Mode in Beta - Feedback" (translated)
  - `Toggle Simple Mode` command → `Toggle App Mode` (translated)

## Languages Updated
en, zh, zh-TW, ja, ko, fr, es, pt-BR, ru, tr, ar, fa

## Notes
Internal variable names (`linearMode`, `canvasStore.linearMode`) remain
unchanged to avoid breaking changes.

Fixes #8577

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Style**
* Renamed application terminology from "Simple Mode" to "App Mode" in
user interface labels, mode descriptions, and mode toggle command.
Updates applied consistently across all 12 supported language
translations to ensure consistent terminology throughout the
application.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8590-feat-update-user-facing-Simple-Mode-terminology-to-App-Mode-2fc6d73d36508160a19af70b228b0a7e)
by [Unito](https://www.unito.io)

src/locales/ar/main.json

@@ -1152,11 +1152,11 @@
     "helpFix": "المساعدة في الإصلاح"
   },
   "linearMode": {
-    "beta": "تجريبي - أرسل ملاحظاتك",
+    "beta": "وضع التطبيق تجريبي - أرسل ملاحظاتك",
     "downloadAll": "تنزيل الكل",
     "dragAndDropImage": "اسحب وأسقط صورة",
     "graphMode": "وضع الرسم البياني",
-    "linearMode": "الوضع البسيط",
+    "linearMode": "وضع التطبيق",
     "rerun": "تشغيل مجدد",
     "reuseParameters": "إعادة استخدام المعلمات",
     "runCount": "عدد مرات التشغيل:"
@@ -1648,7 +1648,7 @@
     "Toggle Logs Bottom Panel": "تبديل لوحة السجلات السفلية",
     "Toggle Queue Panel V2": "تبديل لوحة قائمة الانتظار V2",
     "Toggle Search Box": "تبديل مربع البحث",
-    "Toggle Simple Mode": "تبديل وضع البسيط",
+    "Toggle App Mode": "تبديل وضع التطبيق",
     "Toggle Terminal Bottom Panel": "تبديل لوحة الطرفية السفلية",
     "Toggle Theme (Dark/Light)": "تبديل السمة (داكن/فاتح)",
     "Toggle View Controls Bottom Panel": "تبديل لوحة عناصر التحكم في العرض السفلية",