Deprecate removed browse/discovery endpoints

[wardbox]

Context

Part of the Spotify Feb 2026 API changes (#70). These endpoints are removed with no replacement:

• GET /browse/new-releases ❌
• GET /browse/categories ❌
• GET /browse/categories/{id} ❌ (includes category playlists)
• GET /artists/{id}/top-tracks ❌

Files affected (4)

• Spotishell/Public/Browse/Get-NewReleases.ps1
• Spotishell/Public/Browse/Get-Category.ps1
• Spotishell/Public/Browse/Get-CategoryPlaylists.ps1
• Spotishell/Public/Artists/Get-ArtistTopTracks.ps1

Decision needed

• Option A: Remove these cmdlets entirely and note in changelog
• Option B: Keep them but add deprecation warnings that explain the API no longer supports these
• Either way, update module manifest to remove exports