Fix portable profile storage

[Vaso73]

Fixes issue #74.

Summary:

• stores profiles.json in Flow Launchers per-plugin settings directory
• migrates legacy ~/.ssh/profiles.json into the new plugin settings path when needed
• documents portable/profile storage behavior
• adds storage-path regression coverage

Validation:

• runtime portable test PASS
• profile saved to UserData\Settings\Plugins\Flow.Launcher.Plugin.QuickSSH\profiles.json
• existing C:\Users\info.ssh\profiles.json unchanged
• test profile cleaned up after validation
• server-side Linux dotnet test could not run because Microsoft.WindowsDesktop.App 9.0 runtime is unavailable on Linux; GitHub CI runs on windows-latest