chore: repo scaffold, READMEs (EN/pt-BR), version pins, source fetch+vendorize scripts

- pins OpenBSD 8.0 tarballs (sha256) and Linux 7.3.4 as the port targets
- scripts/fetch-sources.sh (C3SL primary, cdn fallback), scripts/vendorize.sh
- scripts/{kernel-config,build-kernel}.sh for the VM-lab kernel

scripts/kernel-config.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Configure the Linux 7.3.4 tree for PF-on-Linux VM lab use:
+# defconfig baseline + direct-kernel-boot deps. Idempotent.
+# `kernel-config.sh test` additionally enables DEBUG_KMEMLEAK (soak builds).
+set -euo pipefail
+K="${KERNELDIR:-$(cd "$(dirname "$0")/../../linux_kernel/linux-7.3.4" && pwd)}"
+cd "$K"
+[ -f .config ] || make defconfig
+scripts/config --file .config \
+  --set-val CONFIG_VIRTIO_BLK y \
+  --set-val CONFIG_VIRTIO_PCI y \
+  --set-val CONFIG_VIRTIO_NET y \
+  --set-val CONFIG_EXT4_FS y \
+  --set-val CONFIG_NETFILTER y \
+  --enable  CONFIG_NETFILTER_ADVANCED \
+  --set-val CONFIG_NET_SCHED y \
+  --set-val CONFIG_INET y \
+  --set-val CONFIG_IPV6 y \
+  --set-val CONFIG_SERIAL_8250 y \
+  --enable  CONFIG_SERIAL_8250_CONSOLE
+if [ "${1:-}" = "test" ]; then
+  scripts/config --file .config --set-val CONFIG_DEBUG_INFO y --enable CONFIG_DEBUG_KMEMLEAK
+fi
+make olddefconfig
+echo "--- effective ---"
+grep -E '^(CONFIG_VIRTIO_(BLK|PCI|NET)|CONFIG_EXT4_FS|CONFIG_NETFILTER|CONFIG_NET_SCHED|CONFIG_INET|CONFIG_IPV6|CONFIG_DEBUG_KMEMLEAK)(=| is not)' .config || true