Migrate user endpoints to /me equivalents

[wardbox]

Context

Part of the Spotify Feb 2026 API changes (#70). These user endpoints are removed:

• GET /users/{id} ❌ → use GET /me
• GET /users/{id}/playlists ❌ → use GET /me/playlists
• POST /users/{user_id}/playlists ❌ → use POST /me/playlists
• GET /markets ❌ (no replacement)

Files affected (3)

• Spotishell/Public/Users Profile/Get-UserProfile.ps1 — can only get current user now
• Spotishell/Public/Playlists/Get-UserPlaylists.ps1 — must use /me/playlists
• Spotishell/Public/Playlists/New-Playlist.ps1 — must use /me/playlists instead of /users/{id}/playlists

Notes

• Get-UserProfile loses the ability to look up other users — may need parameter changes or deprecation of the UserId parameter
• New-Playlist currently requires a UserId; should default to current user via /me