Deprecate: redirect to Lyrics Karaoke

[mogul]

Reconstructed from slopsmith/slopsmith-plugin-lyrics-sync#1 — original PR by @byrongamatos. Applied as the PR's end-state onto the current main (the original branch no longer cherry-picks cleanly after the redaction squash); commit retains original authorship. Redirect link repointed to got-feedback.

Summary

This plugin has merged into Lyrics Karaoke. The Whisper alignment workflow now lives there alongside per-syllable pitch extraction and the in-player karaoke ribbon, so karaoke setup is a single screen end-to-end.

This PR reduces the plugin to a soft-redirect stub:

• routes.py removed — /align, /save, /export moved to the merged plugin under /api/plugins/lyrics_karaoke/...
• screen.html replaced with a "moved" page + manual "Open Lyrics Karaoke" fallback button
• screen.js wraps showScreen to auto-redirect, but only when the merged plugin's screen is actually present in the DOM (stub-only installs still see the manual button)
• plugin.json name + nav label updated to "Lyrics Sync (moved)" so the redirect is signposted; routes field removed
• README deprecation banner

Test plan

• Install both this plugin and the new Lyrics Karaoke plugin → click "Lyrics Sync" in the sidebar → auto-redirected to the Lyrics Karaoke screen.
• Install only this plugin → "Lyrics Sync" sidebar entry shows the moved page; clicking the button does nothing (no merged plugin to redirect to), but the page is the user's signal to install Lyrics Karaoke.
• No plugin loader errors on startup (no routes.py is fine — the field is optional).

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