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/songs/route.ts

@@ -0,0 +1,49 @@
+import { NextRequest, NextResponse } from "next/server";
+import { searchSongs as searchSongsDB, upsertSong } from "@/lib/db/client";
+import { searchSongs as searchMB } from "@/lib/musicbrainz/client";
+import { z } from "zod";
+
+const QuerySchema = z.object({
+  q: z.string().min(1).max(200),
+  limit: z.coerce.number().int().min(1).max(50).default(20),
+});
+
+export async function GET(req: NextRequest) {
+  const params = Object.fromEntries(req.nextUrl.searchParams);
+  const parsed = QuerySchema.safeParse(params);
+
+  if (!parsed.success) {
+    return NextResponse.json(
+      { error: "Invalid query parameters", details: parsed.error.flatten() },
+      { status: 400 }
+    );
+  }
+
+  const { q, limit } = parsed.data;
+
+  // Try local DB first
+  let songs = await searchSongsDB(q, limit);
+
+  // Augment from MusicBrainz when local results are thin
+  if (songs.length < 3) {
+    try {
+      const mbResults = await searchMB(q, limit);
+      for (const s of mbResults) {
+        await upsertSong({
+          mbid: s.mbid,
+          title: s.title,
+          artist: s.artist,
+          duration_seconds: s.duration_seconds,
+          acousticbrainz_bpm: null,
+          acousticbrainz_time_sig_num: null,
+          source: "musicbrainz",
+        });
+      }
+      songs = await searchSongsDB(q, limit);
+    } catch (err) {
+      console.error("[songs] MusicBrainz search failed:", err);
+    }
+  }
+
+  return NextResponse.json({ songs, total: songs.length });
+}