Armbian 25.11.1

This release advances Armbian on three fronts: more boards now run on mainline-based firmware with BTRFS boot support; hardware coverage has grown significantly across multiple vendors; and the build framework has been upgraded with mmdebstrap, the lowmem extension, first-boot configuration injection, improved release logging, and more robust keyring and mirror handling. In our continued push toward mainline kernel support across our board portfolio, this release marks a significant milestone - the progressive retirement of vendor-specific boot loaders on several boards.