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>

app/api/tracks/route.ts

@@ -0,0 +1,80 @@
+import { NextRequest, NextResponse } from "next/server";
+import { z } from "zod";
+import { getTempoMapsForSong, insertTempoMap, query } from "@/lib/db/client";
+import { validateCTP } from "@/lib/ctp/validate";
+
+// ─── GET /api/tracks?mbid=<uuid> ─────────────────────────────────────────────
+
+const GetSchema = z.object({
+  mbid: z.string().uuid(),
+});
+
+export async function GET(req: NextRequest) {
+  const params = Object.fromEntries(req.nextUrl.searchParams);
+  const parsed = GetSchema.safeParse(params);
+
+  if (!parsed.success) {
+    return NextResponse.json(
+      { error: "mbid (UUID) is required" },
+      { status: 400 }
+    );
+  }
+
+  const maps = await getTempoMapsForSong(parsed.data.mbid);
+  return NextResponse.json({ maps });
+}
+
+// ─── POST /api/tracks ─────────────────────────────────────────────────────────
+// Body: a raw CTP document JSON
+
+export async function POST(req: NextRequest) {
+  let body: unknown;
+  try {
+    body = await req.json();
+  } catch {
+    return NextResponse.json({ error: "Invalid JSON body" }, { status: 400 });
+  }
+
+  const validation = validateCTP(body);
+  if (!validation.success) {
+    return NextResponse.json(
+      {
+        error: "CTP document validation failed",
+        details: validation.errors.flatten(),
+      },
+      { status: 422 }
+    );
+  }
+
+  const doc = validation.data;
+
+  if (!doc.metadata.mbid) {
+    return NextResponse.json(
+      { error: "CTP document must include a metadata.mbid to be stored" },
+      { status: 422 }
+    );
+  }
+
+  // Ensure the song exists
+  const { rowCount } = await query("SELECT 1 FROM songs WHERE mbid = $1", [
+    doc.metadata.mbid,
+  ]);
+
+  if (!rowCount || rowCount === 0) {
+    return NextResponse.json(
+      {
+        error: "Song not found. Search for the song first to register it.",
+        mbid: doc.metadata.mbid,
+      },
+      { status: 404 }
+    );
+  }
+
+  const map = await insertTempoMap({
+    song_mbid: doc.metadata.mbid,
+    ctp_data: body as Record<string, unknown>,
+    contributed_by: doc.metadata.contributed_by,
+  });
+
+  return NextResponse.json({ map }, { status: 201 });
+}