build: collect ISO and logs under versioned dist/easy-bee-v{VERSION}/ dir

All final artefacts for a given version now land in one place:
  dist/easy-bee-v4.1/
    easy-bee-nvidia-v4.1-amd64.iso
    easy-bee-nvidia-v4.1-amd64.logs.tar.gz   ← log archive
                                               (logs dir deleted after archiving)

- Introduce OUT_DIR="${DIST_DIR}/easy-bee-v${ISO_VERSION_EFFECTIVE}"
- Move LOG_DIR, LOG_ARCHIVE, and ISO_OUT into OUT_DIR
- cleanup_build_log: use dirname(LOG_DIR) as tar -C base so the path is
  correct regardless of where OUT_DIR lives; delete LOG_DIR after archiving

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/build.sh

@@ -591,9 +591,12 @@ recover_iso_memtest() {
 AUDIT_VERSION_EFFECTIVE="$(resolve_audit_version)"
 ISO_VERSION_EFFECTIVE="$(resolve_iso_version)"
 ISO_BASENAME="easy-bee-${BEE_GPU_VENDOR}-v${ISO_VERSION_EFFECTIVE}-amd64"
-LOG_DIR="${DIST_DIR}/${ISO_BASENAME}.logs"
-LOG_ARCHIVE="${DIST_DIR}/${ISO_BASENAME}.logs.tar.gz"
-ISO_OUT="${DIST_DIR}/${ISO_BASENAME}.iso"
+# Versioned output directory: dist/easy-bee-v4.1/ — all final artefacts live here.
+OUT_DIR="${DIST_DIR}/easy-bee-v${ISO_VERSION_EFFECTIVE}"
+mkdir -p "${OUT_DIR}"
+LOG_DIR="${OUT_DIR}/${ISO_BASENAME}.logs"
+LOG_ARCHIVE="${OUT_DIR}/${ISO_BASENAME}.logs.tar.gz"
+ISO_OUT="${OUT_DIR}/${ISO_BASENAME}.iso"
 LOG_OUT="${LOG_DIR}/build.log"
 
 cleanup_build_log() {
@@ -616,7 +619,8 @@ cleanup_build_log() {
 
     if [ -n "${LOG_DIR:-}" ] && [ -d "${LOG_DIR}" ] && command -v tar >/dev/null 2>&1; then
         rm -f "${LOG_ARCHIVE}"
-        tar -czf "${LOG_ARCHIVE}" -C "${DIST_DIR}" "$(basename "${LOG_DIR}")" 2>/dev/null || true
+        tar -czf "${LOG_ARCHIVE}" -C "$(dirname "${LOG_DIR}")" "$(basename "${LOG_DIR}")" 2>/dev/null || true
+        rm -rf "${LOG_DIR}"
     fi
 
     exit "${status}"