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>

lib/db/schema.sql

@@ -0,0 +1,99 @@
+-- ClickTrack PostgreSQL schema
+-- Run via: psql $DATABASE_URL -f lib/db/schema.sql
+-- Or applied automatically by docker/init.sql on first container start.
+
+-- Enable UUID generation
+CREATE EXTENSION IF NOT EXISTS "pgcrypto";
+
+-- ─── songs ────────────────────────────────────────────────────────────────────
+-- Canonical song records, populated from MusicBrainz lookups and/or
+-- community contributions. mbid is the MusicBrainz Recording UUID.
+
+CREATE TABLE IF NOT EXISTS songs (
+  mbid               UUID          PRIMARY KEY,
+  title              TEXT          NOT NULL,
+  artist             TEXT          NOT NULL,
+  -- Duration in seconds as reported by MusicBrainz
+  duration_seconds   NUMERIC(8, 3),
+  -- AcousticBrainz / AcousticBrainz-derived BPM estimate (nullable)
+  acousticbrainz_bpm NUMERIC(6, 2),
+  -- AcousticBrainz time signature numerator (e.g. 4 for 4/4)
+  acousticbrainz_time_sig_num INTEGER,
+  -- How this record was created: 'musicbrainz' | 'manual' | 'registry'
+  source             TEXT          NOT NULL DEFAULT 'musicbrainz',
+  created_at         TIMESTAMPTZ   NOT NULL DEFAULT NOW(),
+  updated_at         TIMESTAMPTZ   NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS songs_title_artist_idx
+  ON songs USING gin(to_tsvector('english', title || ' ' || artist));
+
+-- ─── tempo_maps ───────────────────────────────────────────────────────────────
+-- Community-contributed CTP documents for a given song.
+-- Multiple maps per song are allowed; clients pick the highest-voted verified one.
+
+CREATE TABLE IF NOT EXISTS tempo_maps (
+  id             UUID          PRIMARY KEY DEFAULT gen_random_uuid(),
+  song_mbid      UUID          NOT NULL REFERENCES songs(mbid) ON DELETE CASCADE,
+  -- Full CTP document stored as JSONB for flexible querying
+  ctp_data       JSONB         NOT NULL,
+  contributed_by TEXT          NOT NULL,
+  verified       BOOLEAN       NOT NULL DEFAULT FALSE,
+  upvotes        INTEGER       NOT NULL DEFAULT 0,
+  created_at     TIMESTAMPTZ   NOT NULL DEFAULT NOW(),
+  updated_at     TIMESTAMPTZ   NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS tempo_maps_song_mbid_idx ON tempo_maps (song_mbid);
+CREATE INDEX IF NOT EXISTS tempo_maps_verified_upvotes_idx
+  ON tempo_maps (verified DESC, upvotes DESC);
+
+-- Ensure ctp_data contains at least a version field
+ALTER TABLE tempo_maps
+  ADD CONSTRAINT ctp_data_has_version
+  CHECK (ctp_data ? 'version');
+
+-- ─── registry_sync_log ────────────────────────────────────────────────────────
+-- Audit log for Git registry sync operations.
+
+CREATE TABLE IF NOT EXISTS registry_sync_log (
+  id              UUID          PRIMARY KEY DEFAULT gen_random_uuid(),
+  synced_at       TIMESTAMPTZ   NOT NULL DEFAULT NOW(),
+  records_added   INTEGER       NOT NULL DEFAULT 0,
+  records_updated INTEGER       NOT NULL DEFAULT 0,
+  -- 'success' | 'partial' | 'failed'
+  status          TEXT          NOT NULL,
+  -- Error message or notes
+  message         TEXT
+);
+
+-- ─── Helpers ──────────────────────────────────────────────────────────────────
+
+-- Auto-update updated_at columns via trigger
+CREATE OR REPLACE FUNCTION set_updated_at()
+RETURNS TRIGGER LANGUAGE plpgsql AS $$
+BEGIN
+  NEW.updated_at = NOW();
+  RETURN NEW;
+END;
+$$;
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_trigger WHERE tgname = 'songs_set_updated_at'
+  ) THEN
+    CREATE TRIGGER songs_set_updated_at
+      BEFORE UPDATE ON songs
+      FOR EACH ROW EXECUTE FUNCTION set_updated_at();
+  END IF;
+
+  IF NOT EXISTS (
+    SELECT 1 FROM pg_trigger WHERE tgname = 'tempo_maps_set_updated_at'
+  ) THEN
+    CREATE TRIGGER tempo_maps_set_updated_at
+      BEFORE UPDATE ON tempo_maps
+      FOR EACH ROW EXECUTE FUNCTION set_updated_at();
+  END IF;
+END;
+$$;