feat: initial scaffold for ClickTrack monorepo

Full self-hosted click track generator for cover bands.

Core technical pieces implemented:
- CTP (Click Track Protocol) TypeScript schema, Zod validator, and WAV
  renderer (44.1 kHz, 16-bit PCM, accented downbeats, ramp sections)
- MusicBrainz API client with 1 req/s rate limiting
- PostgreSQL schema (songs, tempo_maps, registry_sync_log) with triggers
- Git registry sync logic (clone/pull → validate CTP → upsert DB)
- Next.js 14 App Router: search page, track page, API routes
  (/api/songs, /api/tracks, /api/generate)
- UI components: SearchBar, SongResult, TempoMapEditor, ClickTrackPlayer
  (Web Audio API in-browser playback + WAV download)
- Docker Compose stack: app + postgres + redis + nginx + registry-sync
- Multi-stage Dockerfile with standalone Next.js output
- .env.example documenting all configuration variables
- README with setup instructions, CTP format spec, and API reference

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile

@@ -0,0 +1,61 @@
+# syntax=docker/dockerfile:1
+
+# ────────────────────────────────────────────────────────────────────────────────
+# Stage 1 — deps: install all node_modules
+# ────────────────────────────────────────────────────────────────────────────────
+FROM node:20-alpine AS deps
+
+RUN apk add --no-cache libc6-compat git
+
+WORKDIR /app
+
+COPY package.json package-lock.json* yarn.lock* pnpm-lock.yaml* ./
+
+RUN \
+  if [ -f package-lock.json ]; then npm ci; \
+  elif [ -f yarn.lock ]; then yarn --frozen-lockfile; \
+  elif [ -f pnpm-lock.yaml ]; then corepack enable pnpm && pnpm install --frozen-lockfile; \
+  else echo "No lockfile found." && npm install; \
+  fi
+
+# ────────────────────────────────────────────────────────────────────────────────
+# Stage 2 — builder: compile Next.js production build
+# ────────────────────────────────────────────────────────────────────────────────
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+# Disable Next.js telemetry during build
+ENV NEXT_TELEMETRY_DISABLED=1
+
+RUN npm run build
+
+# ────────────────────────────────────────────────────────────────────────────────
+# Stage 3 — runner: minimal production image
+# ────────────────────────────────────────────────────────────────────────────────
+FROM node:20-alpine AS runner
+
+WORKDIR /app
+
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
+
+RUN addgroup --system --gid 1001 nodejs \
+ && adduser  --system --uid 1001 nextjs
+
+# Copy only what's needed to run
+COPY --from=builder /app/public            ./public
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static     ./.next/static
+
+USER nextjs
+
+EXPOSE 3000
+
+ENV PORT=3000
+ENV HOSTNAME="0.0.0.0"
+
+CMD ["node", "server.js"]