v2026.01.26

• Use .unpacked stamp files for source dependencies instead of directories
  to prevent unnecessary rebuilds when builds modify source trees
• Hardcode checksums in Makefile instead of downloading from same server as tarballs
• Use Docker for all Linux builds (both on macOS and Linux) for reproducibility
• Fix gawk/grep lipo race condition by depending on directory targets with recipes
• Fix toybox parallel build race by clearing MAKEFLAGS before sub-make
• Fix clean_dist to fully remove directory instead of just contents
• Add component/platform validity matrix to prevent invalid target generation
• Simplify UNIVERSAL_DARWIN_COMPONENTS to use COMMON_COMPONENTS directly
• Add docker_platform helper for consistent Docker platform naming
• Update README with Docker requirements and OrbStack as alternative
• Disable busybox CONFIG_TC and SHA hardware acceleration on aarch64
• Add macOS SDK 26.2
• Bump versions