chore(release): archive ISO build recipes, tarball-only releases

Releases no longer ship as bootable ISOs. Archipelago updates are
distributed as the backend binary plus a frontend tarball referenced by
releases/manifest.json. Nodes OTA-update via scripts/self-update.sh.

Filebrowser and AIUI remain bundled inside the frontend tarball and
deployed atomically, verified present in v1.7.43-alpha release artifact
(189 AIUI files, filebrowser-client bundle).

Archived under image-recipe/_archived/ (resurrectable if ISO distribution
is reintroduced):
  - build-auto-installer-iso.sh
  - build-unbundled-iso.sh
  - test-iso-qemu.sh
  - scripts/convert-iso-to-disk.sh
  - BUILD-ISO-STATUS.md, ISO-BUILD-CHECKLIST.md
  - branding/isohdpfx.bin
  - .gitea/workflows/build-iso-dev.yml

Updated release process docs to drop ISO references:
  - scripts/create-release.sh (next-steps text)
  - docs/BETA-RELEASE-CHECKLIST.md
  - docs/hotfix-process.md
  - README.md

image-recipe/_archived/build-unbundled-iso.sh

@@ -0,0 +1,33 @@
+#!/bin/bash
+#
+# Build Archipelago UNBUNDLED Auto-Installer ISO
+#
+# Same as build-auto-installer-iso.sh but WITHOUT pre-bundled container images.
+# Users install all apps on-demand from the Marketplace (requires internet).
+#
+# Benefits:
+#   - Much smaller ISO (~1-2GB vs ~8-10GB)
+#   - Faster build (no image pulling/saving)
+#   - Faster install (no image copying/loading)
+#
+# Trade-offs:
+#   - Internet required after first boot to install apps
+#   - No apps pre-loaded — everything comes from Marketplace
+#
+# Usage:
+#   sudo ./build-unbundled-iso.sh
+#   DEV_SERVER=archipelago@192.168.1.228 sudo ./build-unbundled-iso.sh
+#   BUILD_FROM_SOURCE=1 sudo ./build-unbundled-iso.sh
+#
+
+set -e
+
+# Configuration
+DEV_SERVER="${DEV_SERVER:-archipelago@192.168.1.228}"
+BUILD_FROM_SOURCE="${BUILD_FROM_SOURCE:-0}"
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+
+# Delegate to the main build script with UNBUNDLED mode
+export UNBUNDLED=1
+exec "$SCRIPT_DIR/build-auto-installer-iso.sh" "$@"