feat: validate boot option in runners configuration for native runners

preflight.sh

@@ -183,6 +183,17 @@ check_runners_ini_format() {
       fi
     fi
 
+    # boot: must be "true" or "false" if present (native runners only)
+    local boot
+    boot=$(ini_get "$conf" "$section" "boot" "")
+    if [[ -n "$boot" ]] && [[ "$boot" != "true" ]] && [[ "$boot" != "false" ]]; then
+      log_error "  → [$section] boot='$boot' (must be 'true' or 'false')"
+      errors=$((errors + 1))
+    fi
+    if [[ "$boot" == "true" ]] && [[ "$type" == "docker" ]]; then
+      log_warn "  → [$section] boot=true has no effect on docker runners (ignored)"
+    fi
+
     # docker runner: default_image should be set
     if [[ "$type" == "docker" ]]; then
       local default_image