Phase 4: drone + T6/E-series + polish + deploy + README

Add drone synth + DronePlayer, wire T6 (mode over drone) and E1-E3 info pages
(E3 carries a drone). Screen Wake Lock while any click/drone plays. Vitest suite
for scheduler timing (no drift over 5 min) and music-layer correctness (triads,
CAGED, diatonic, fretboard). Deploy artifacts: public/_redirects, multi-stage
Dockerfile + nginx.conf (SPA fallback, immutable asset caching, gzip),
.dockerignore. README covering build, Cloudflare Pages / nginx / Docker deploy,
and the deep-link URL format. prefers-reduced-motion honored throughout.

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

nginx/default.conf

@@ -0,0 +1,27 @@
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    gzip on;
+    gzip_types text/css application/javascript application/json image/svg+xml;
+    gzip_min_length 1024;
+
+    # Hashed build assets are immutable — cache hard.
+    location /assets/ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+        try_files $uri =404;
+    }
+
+    # Never cache the HTML shell so new deploys are picked up.
+    location = /index.html {
+        add_header Cache-Control "no-cache";
+    }
+
+    # SPA fallback: path-routed deep links (e.g. /drill/R3) must serve the app.
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+}