Refactor batch fetch endpoints to individual calls

[wardbox]

Context

Part of the Spotify Feb 2026 API changes (#70). Multi-ID batch fetch endpoints are removed:

• GET /tracks?ids= ❌
• GET /albums?ids= ❌
• GET /artists?ids= ❌
• GET /episodes?ids= ❌
• GET /shows?ids= ❌

Must fetch individually by ID (e.g., GET /tracks/{id}).

Files affected (5)

• Spotishell/Public/Tracks/Get-Track.ps1
• Spotishell/Public/Albums/Get-Album.ps1
• Spotishell/Public/Artists/Get-Artist.ps1
• Spotishell/Public/Episodes/Get-Episode.ps1
• Spotishell/Public/Shows/Get-Show.ps1

Notes

• These cmdlets currently accept arrays of IDs and batch them into single API calls
• Need to refactor to loop individual /{type}/{id} calls when multiple IDs are provided
• Single ID path (e.g., /tracks/{id}) should still work — only the batch variant is removed
• Consider performance impact: what was 1 API call for 50 tracks becomes 50 calls