Initial commit: akai-fetch - AKAI sampler ISO downloader & extractor

- fetch: Go CLI tool for searching, downloading, and extracting
  AKAI sampler ISOs from archive.org
- scripts/extract_wavs.sh: Shell script driving akaiutil to
  convert samples to WAV
- Dockerfile: Multi-stage build packaging akaiutil + fetch
- third_party/akaiutil: Vendored akaiutil v4.6.7 source (GPLv2)
- docs/akaiutil.md: Full akaiutil reference

Dockerfile

@@ -0,0 +1,33 @@
+# Stage 1: Build akaiutil from source
+FROM debian:11 AS akaiutil-builder
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY third_party/akaiutil/ /src/akaiutil/
+WORKDIR /src/akaiutil
+RUN make
+
+# Stage 2: Build fetch (Go tool)
+FROM golang:1.26-alpine AS fetch-builder
+
+WORKDIR /src
+COPY go.mod main.go /src/
+RUN CGO_ENABLED=0 go build -o /fetch .
+
+# Stage 3: Runtime image
+FROM debian:11-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    bash \
+    ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=akaiutil-builder /src/akaiutil/akaiutil /usr/local/bin/
+COPY --from=fetch-builder /fetch /usr/local/bin/fetch
+COPY scripts/extract_wavs.sh /usr/local/bin/
+
+WORKDIR /data
+ENTRYPOINT ["fetch"]
+CMD ["--help"]