feat: Implement complete Zero OS Alpine Initramfs Builder

- Complete bash framework with strict error handling
- Modular library system (docker, alpine, components, initramfs, kernel, testing)
- Rust component integration (zinit, rfs, mycelium) with musl targeting
- Rootless Docker/Podman support for GitHub Actions
- Centralized configuration in config/build.conf
- 2-stage module loading system
- Strip + UPX optimization for minimal size
- Complete zinit integration replacing OpenRC
- GitHub Actions CI/CD pipeline
- Comprehensive documentation and usage guides

Components:
- Latest stable kernel 6.12.44
- Alpine Linux 3.22 base
- ThreeFold components: zinit, mycelium, rfs, corex
- Target: ~8-12MB final initramfs.cpio.xz

configs/sources.conf

@@ -0,0 +1,10 @@
+# sources.conf - Components to download and build for initramfs
+# Format: TYPE:NAME:URL:VERSION:BUILD_FUNCTION[:EXTRA_OPTIONS]
+
+# Git repositories to clone and build
+git:zinit:https://github.com/threefoldtech/zinit:master:build_zinit
+git:mycelium:https://github.com/threefoldtech/mycelium:0.6.1:build_mycelium
+git:rfs:https://github.com/threefoldtech/rfs:development:build_rfs
+
+# Pre-built releases to download
+release:corex:https://github.com/threefoldtech/corex/releases/download/2.1.4/corex-2.1.4-amd64-linux-static:2.1.4:install_corex:rename=corex