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/generate/route.ts

@@ -0,0 +1,86 @@
+import { NextRequest, NextResponse } from "next/server";
+import { z } from "zod";
+import { query } from "@/lib/db/client";
+import { validateCTP } from "@/lib/ctp/validate";
+import { renderCTP } from "@/lib/ctp/render";
+import type { TempoMapRow } from "@/lib/db/client";
+
+const ParamsSchema = z.object({
+  id: z.string().uuid("tempo map id must be a UUID"),
+  count_in: z
+    .enum(["true", "false"])
+    .transform((v) => v === "true")
+    .optional(),
+});
+
+/**
+ * GET /api/generate?id=<tempo-map-uuid>[&count_in=true]
+ *
+ * Renders the requested tempo map to a WAV file and streams it back.
+ * The response is cached for 1 hour since tempo maps are immutable once created.
+ */
+export async function GET(req: NextRequest) {
+  const raw = Object.fromEntries(req.nextUrl.searchParams);
+  const parsed = ParamsSchema.safeParse(raw);
+
+  if (!parsed.success) {
+    return NextResponse.json(
+      { error: "Invalid parameters", details: parsed.error.flatten() },
+      { status: 400 }
+    );
+  }
+
+  const { id, count_in } = parsed.data;
+
+  // Load tempo map from DB
+  const { rows } = await query<TempoMapRow>(
+    "SELECT * FROM tempo_maps WHERE id = $1",
+    [id]
+  );
+
+  if (rows.length === 0) {
+    return NextResponse.json({ error: "Tempo map not found" }, { status: 404 });
+  }
+
+  const map = rows[0];
+  const validation = validateCTP(map.ctp_data);
+
+  if (!validation.success) {
+    return NextResponse.json(
+      { error: "Stored CTP document is invalid", details: validation.errors.flatten() },
+      { status: 500 }
+    );
+  }
+
+  const doc = validation.data;
+
+  // Render WAV
+  let wav: Buffer;
+  try {
+    wav = renderCTP(doc, { countIn: count_in });
+  } catch (err) {
+    console.error("[generate] Render error:", err);
+    return NextResponse.json(
+      { error: "Failed to render click track", detail: String(err) },
+      { status: 500 }
+    );
+  }
+
+  // Build a clean filename
+  const safeName = `${doc.metadata.artist} - ${doc.metadata.title}`
+    .replace(/[^\w\s\-]/g, "")
+    .replace(/\s+/g, "_")
+    .slice(0, 80);
+
+  const filename = `${safeName}_click.wav`;
+
+  return new NextResponse(wav, {
+    status: 200,
+    headers: {
+      "Content-Type": "audio/wav",
+      "Content-Disposition": `attachment; filename="${filename}"`,
+      "Content-Length": String(wav.byteLength),
+      "Cache-Control": "public, max-age=3600, immutable",
+    },
+  });
+}