feat: modular synth, sandbox, code editor, pixel editor, Docker deployment

Synth:
- Modular synth with Tone.js: oscillator, LFO, noise, filter, envelope, VCA, mixer, delay, reverb, distortion, output
- Keyboard widget (mini SVG + fullscreen piano + computer keys Z-M/Q-I)
- Drum pad (4x4 grid, 16 pads with MIDI notes, matching reaktor)
- Sequencer (SVG bar grid with pitch/gate editing, matching reaktor)
- Live modulation visualization (LFO waveform simulation, envelope, noise)
- Knob with drag, wheel, double-click inline edit, modulation glow ring
- Pan/zoom viewport, bezier wires colored by port type
- Play/Stop audio lifecycle, stereo output with Tone.Merge

Sandbox:
- New /sandbox page with all editors in freeform mode
- Synth fills full viewport height

Workbenches:
- Code Editor (Monaco) with test cases
- Signal Playground (Web Audio oscillator + filter + visualizer)
- Pixel Editor (grid canvas with palette and match mode)

Deployment:
- Dockerfile (multi-stage Next.js standalone build)
- .dockerignore
- next.config.ts output: standalone
- Gitea remote configured

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,20 @@
+# Stage 1: Build
+FROM node:20-alpine AS build
+WORKDIR /app
+COPY package.json package-lock.json* ./
+RUN npm ci --include=dev
+COPY . .
+RUN npm run build
+
+# Stage 2: Production
+FROM node:20-alpine
+WORKDIR /app
+ENV NODE_ENV=production PORT=80
+
+# Copy standalone output
+COPY --from=build /app/.next/standalone ./
+COPY --from=build /app/.next/static ./.next/static
+COPY --from=build /app/public ./public
+
+EXPOSE 80
+CMD ["node", "server.js"]