Modularize Spotify page controller logic

[postigodev]

Summary

Spotify logic is one of the richest parts of the app: auth flow, polling, playback actions, target-device selection, and session rendering.

Why this matters

This code works, but it is still concentrated enough that it raises the cost of changing one area without understanding all of them.

Expected outcome

Split Spotify page/controller logic into smaller pieces while preserving:

• active-view-only polling
• no duplicate intervals
• no stale target-device behavior
• current UI behavior

Likely files

• apps/tauri/src/main.ts
• apps/tauri/src/pages/spotify.ts
• apps/tauri/src/features/*