Reduce Discord RPC polling churn

[valipuha]

Summary

• collapse the Apple Music polling path into a single JXA status call per loop
• avoid re-sending identical Discord activity unless the track changes, playback position jumps, or temporary artwork expires
• remove hot-loop reconnect/state logging so the background service does less steady-state work

Why

Issue #88 reports that the process RSS keeps growing over long runs even when heap snapshots do not show a clear JavaScript leak. This change reduces the two biggest sources of steady-state churn in the loop: repeated osascript invocations and repeated Discord RPC/log updates for the same track.

Validation

• deno fmt --check music-rpc.ts
• deno lint
• deno check --allow-import music-rpc.ts