Phase 1: scaffold + metronome engine + R1

Svelte 5 + Vite static SPA with absolute base and History-API path routing.
Core lookahead-scheduler metronome (no drift), AudioContext unlock-on-gesture,
synthesized 3-voice clicks, rAF-synced beat highlight. StrumGrid renderer and
R1 wired end-to-end with variants, BPM/variant persistence, query overrides,
and keyboard shortcuts (space, arrow up/down). Dark amp-light theme tokens.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

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+node_modules
+dist
+.DS_Store
+*.local
+.vite