Extend Library module: saved shows and episodes

[guidefari]

Summary

Extend the Library module with saved shows and episodes endpoints.

Context

Library module currently handles saved albums and tracks. Spotify API also supports:

• GET /me/shows — get saved shows
• PUT /me/shows — save shows
• DELETE /me/shows — remove saved shows
• GET /me/episodes — get saved episodes
• PUT /me/episodes — save episodes
• DELETE /me/episodes — remove saved episodes

removeSavedShows already exists but the corresponding get/save and all episode methods are missing.

Acceptance criteria

• getSavedShows(), saveShows() added to Library
• getSavedEpisodes(), saveEpisodes(), removeSavedEpisodes() added to Library
• areShowsSaved(), areEpisodesSaved() check methods added

Related

PRD #9, depends on #30 and #31 for model types

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Migrated from guidefari/spotify-effect#50