chore(phase-0): stabilise foundation for Studio build

- Extract WAV assembly (buildWav, mergeFloat32Arrays, decodeFloat32Chunk,
  SAMPLE_RATE) into web/lib/audio/wav.ts so it can be reused by the
  Studio playback engine and library waveform previews
- Add server/waveform.py with compute_peaks() / write_peaks() — reads
  any WAV, mixes to mono, returns min/max peak arrays matching the
  WaveformPeaks TypeScript type
- Add server/ids.py with prefixed URL-safe ID helpers (gen_id, proj_id,
  asset_id, etc.) using stdlib secrets — no new dependency
- Add docs/studio-build-plan.md — full execution spec covering stack
  decisions, data models, API contract, component hierarchy, phase
  breakdown and acceptance criteria
- Ignore data/ directory (generated audio, waveforms, SQLite DB)

web/lib/audio/wav.ts

@@ -0,0 +1,56 @@
+export const SAMPLE_RATE = 24_000;
+
+export function decodeFloat32Chunk(data: string): Float32Array<ArrayBuffer> {
+  const raw = atob(data);
+  const bytes = new Uint8Array(raw.length);
+  for (let i = 0; i < raw.length; i += 1) {
+    bytes[i] = raw.charCodeAt(i);
+  }
+  return new Float32Array(bytes.buffer as ArrayBuffer);
+}
+
+export function mergeFloat32Arrays(
+  chunks: Float32Array<ArrayBuffer>[]
+): Float32Array<ArrayBuffer> {
+  const total = chunks.reduce((sum, chunk) => sum + chunk.length, 0);
+  const out = new Float32Array(total);
+  let offset = 0;
+  for (const chunk of chunks) {
+    out.set(chunk, offset);
+    offset += chunk.length;
+  }
+  return out;
+}
+
+/** Builds a float32 RIFF/WAV Blob from raw PCM samples. */
+export function buildWav(
+  samples: Float32Array<ArrayBuffer>,
+  sampleRate: number
+): Blob {
+  const dataSize = samples.length * 4;
+  const buffer = new ArrayBuffer(44 + dataSize);
+  const view = new DataView(buffer);
+
+  const writeString = (offset: number, value: string) => {
+    for (let i = 0; i < value.length; i += 1) {
+      view.setUint8(offset + i, value.charCodeAt(i));
+    }
+  };
+
+  writeString(0, "RIFF");
+  view.setUint32(4, 36 + dataSize, true);
+  writeString(8, "WAVE");
+  writeString(12, "fmt ");
+  view.setUint32(16, 16, true);
+  view.setUint16(20, 3, true); // PCM float32
+  view.setUint16(22, 1, true); // mono
+  view.setUint32(24, sampleRate, true);
+  view.setUint32(28, sampleRate * 4, true); // byte rate
+  view.setUint16(32, 4, true); // block align
+  view.setUint16(34, 32, true); // bits per sample
+  writeString(36, "data");
+  view.setUint32(40, dataSize, true);
+  new Float32Array(buffer, 44).set(samples);
+
+  return new Blob([buffer], { type: "audio/wav" });
+}