feat: update Spotify auth flow for new token handling

[iamGaven]

• Updated Spotify authentication to support new token handling mechanism
• Added instructions and prompt for users to enter their credentials
• Updated project dependencies

[Copilot]

Copilot reviewed 4 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (2)

• SpotifySongDownloader/SpotifySongDownloader.csproj: Language not supported
• SpotifySongDownloader/Views/SearchView.xaml: Language not supported

Comments suppressed due to low confidence (1)

SpotifySongDownloader/Services/SpotifyService.cs:271

• The recursive call to getTracks in response to an unauthorized token may lead to an infinite recursion if the token remains invalid. Consider implementing a retry limit or guard to prevent potential stack overflow.

var trackList2 = await getTracks(playlistID);