Fix PortableMode Check Issue

[Jack251970]

From #3982.

Use !File.Exists(Path.Combine(PortableDataPath, DeletionIndicatorFile))) instead of !File.Exists(DeletionIndicatorFile)) so that we can check if deletion indicator file exists.

[Copilot]

Pull Request Overview

Fixes a bug in the portable mode detection logic where the deletion indicator file check was using an incorrect path. The fix ensures that the deletion indicator file is properly located within the portable data directory.

• Corrects the path for checking the deletion indicator file existence
• Adds readonly modifier to static fields for better immutability
• Improves code readability by splitting the condition check across multiple lines

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Flow.Launcher/SettingPages/ViewModels/SettingsPaneGeneralViewModel.cs	Adds readonly modifier to the _portableMode field
Flow.Launcher.Infrastructure/UserSettings/DataLocation.cs	Fixes deletion indicator file path check and adds readonly modifiers to path fields

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[gitstream-cm]

🥷 Code experts: jjw24, onesounds

Jack251970, onesounds have most 👩‍💻 activity in the files.
Jack251970, jjw24 have most 🧠 knowledge in the files.

See details

Flow.Launcher.Infrastructure/UserSettings/DataLocation.cs

Activity based on git-commit:

	Jack251970	onesounds
SEP
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Knowledge based on git-blame:
jjw24: 70%
Jack251970: 20%

Flow.Launcher/SettingPages/ViewModels/SettingsPaneGeneralViewModel.cs

Activity based on git-commit:

	Jack251970	onesounds
SEP	3 additions & 1 deletions
AUG
JUL	8 additions & 8 deletions
JUN	2 additions & 0 deletions
MAY	15 additions & 4 deletions
APR	64 additions & 137 deletions	355 additions & 225 deletions

Knowledge based on git-blame:
Jack251970: 25%

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[gitstream-cm]

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