refactor: migrate to Mantine 9, Turbopack, and React 19

Upgrade the UI stack and default to Turbopack by serving Signalsmith Stretch
from public/vendor instead of bundling it. Fix player modal z-index, Cookies
hydration, and React 19 ref typing while updating Mantine usage to props-first styling.

Author: bgwastu

.gitignore

@@ -39,4 +39,8 @@ next-env.d.ts
 .fallow/
 
 # docker
-data/
+data/
+# generated Signalsmith WASM/AudioWorklet ESM (copied from node_modules)
+/public/vendor/
+/public/stretch-smoke.wav
+/public/SignalsmithStretch.mjs

Dockerfile

@@ -22,7 +22,7 @@ COPY . .
 RUN mkdir -p public
 
 RUN --mount=type=cache,target=/app/.next/cache \
-    npx next build --webpack
+    npm run build
 
 # Production image
 FROM base AS runner