WDY-771: Import installer payloads on WendyOS boot

[zamderax]

Summary

• add a first-boot WendyOS install-config service and recipe, and include it in the base packagegroup
• persist installer payloads into durable storage so Pi 5 works without /data and Jetson can re-apply config after rootfs swaps
• re-apply hostname, Wi-Fi, SSH, injected agent binaries, and cert bundles on boot, and disable the agent updater timer when a custom agent is supplied

Testing

• bash -n recipes-core/wendyos-install-config/files/wendyos-install-config.sh

Notes

• this intentionally does not include the pre-existing local Makefile modification
• end-to-end hardware flash and first-boot validation were not run in this branch