diskOS installer: initial public beta

Flashes the diskOS custom UI onto the FiiO Snowsky Disc over Ingenic mask-ROM USB,
building the image from your own stock firmware. Runs from source via install.sh.

build/build.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+# build.sh - produce the standalone `diskos-installer` executable for THIS host
+# (Linux or macOS). PyInstaller can't cross-build, so run this on each target OS.
+#
+# Prereqs: python3. Everything else is created in a local venv; nothing is
+# installed system-wide.
+#
+# Before building, populate vendor/<os>-<arch>/ with the native tools for this
+# host (see build/README-vendor.md): usbboot, mksquashfs, unsquashfs,
+# my_write5_dram.bin, disc_spl_lpddr3.bin (+ lib/ for any bundled .so/.dylib).
+set -euo pipefail
+cd "$(dirname "$0")/.."          # installer/
+
+VENV=build/venv
+[ -d "$VENV" ] || python3 -m venv "$VENV"
+"$VENV/bin/pip" install --quiet --upgrade pip pyinstaller pyusb pycryptodome
+
+# sanity: the vendor dir for this host must exist
+tag=$("$VENV/bin/python" - <<'PY'
+import platform
+s=platform.system().lower(); o={"darwin":"macos","linux":"linux"}.get(s,s)
+m=platform.machine().lower()
+a={"x86_64":"x86_64","amd64":"x86_64","arm64":"arm64","aarch64":"arm64"}.get(m,m)
+print(f"{o}-{a}")
+PY
+)
+[ -d "vendor/$tag" ] || { echo "ERROR: vendor/$tag missing - add native tools for this host first." >&2; exit 2; }
+
+"$VENV/bin/pyinstaller" --clean --noconfirm \
+  --distpath build/dist --workpath build/work \
+  build/diskos-installer.spec
+
+echo
+echo "Built: build/dist/diskos-installer  ($(du -h build/dist/diskos-installer | cut -f1))"
+echo "Smoke test: build/dist/diskos-installer doctor"