Add errors for install dir edge cases (#6733)

## Summary
- show explicit validation errors when the install path lives inside the
desktop app bundle or updater cache
- include the new locale strings for these error prompts so the UI
surfaces actionable guidance

## Testing
- pnpm typecheck
- pnpm lint:fix

## Notes
Desktop types still need to be updated to include the new validation
flags; see https://github.com/Comfy-Org/desktop/pull/1400

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6733-Add-errors-for-install-dir-edge-cases-2af6d73d3650811bada6fc7dd72ecf68)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -504,6 +504,8 @@
     "cannotWrite": "Unable to write to the selected path",
     "insufficientFreeSpace": "Insufficient space - minimum free space",
     "isOneDrive": "OneDrive is not supported. Please install ComfyUI in another location.",
+    "insideAppInstallDir": "This folder is inside the ComfyUI Desktop application bundle and will be deleted during updates. Choose a directory outside the install folder, such as Documents/ComfyUI.",
+    "insideUpdaterCache": "This folder is inside the ComfyUI updater cache, which is cleared on every update. Select a different location for your data.",
     "nonDefaultDrive": "Please install ComfyUI on your system drive (eg. C:\\). Drives with different file systems may cause unpredicable issues. Models and other files can be stored on other drives after installation.",
     "parentMissing": "Path does not exist - create the containing directory first",
     "unhandledError": "Unknown error",