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>

tsconfig.json

@@ -0,0 +1,18 @@
+{
+  "extends": "@tsconfig/svelte/tsconfig.json",
+  "compilerOptions": {
+    "target": "ESNext",
+    "useDefineForClassFields": true,
+    "module": "ESNext",
+    "resolveJsonModule": true,
+    "allowJs": true,
+    "checkJs": true,
+    "isolatedModules": true,
+    "moduleResolution": "bundler",
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "sourceMap": true
+  },
+  "include": ["src/**/*.ts", "src/**/*.svelte", "vite.config.ts"]
+}