Offline scrobble queue

[boldandbrad]

Describe the problem
Scrobbles fail when offline, causing users to lose listening data.

Describe the solution you'd like
Add a local queue that:

• Stores pending scrobbles in ~/.spin/queue/ (or platform equivalent)
• Automatically attempts to submit queued scrobbles when a scrobble is attempted
• New spin queue command to view/clear pending scrobbles

Example:

spin track "Radiohead" "Paranoid Android"
"Queued for later submission"

# When online and running any scrobble command:
spin track "Pink Floyd" "Comfortably Numb"
"Submitted 3 queued scrobbles"
"Scrobbled: Pink Floyd - Comfortably Numb"

spin queue list
 1. Radiohead - Paranoid Android (2026-04-13 15:00)

Describe alternatives you've considered
None - losing scrobbles is unacceptable.

Additional context/considerations

• Queue storage format: JSON lines in a file
• Need to handle duplicate timestamps gracefully
• Should have max queue size to prevent unbounded growth