feat: Add custom kernel 6.17.13 build infrastructure

- kernel/build-kernel.sh: Full rebuild script (deps, download, rebrand, compile)
- kernel/configs/config-6.17.13-nullsec: Production kernel config
- kernel/test-kernel-vm.sh: VM testing automation
- kernel/SHA256SUMS: Package integrity checksums
- kernel/README.md: Comprehensive kernel documentation
- Updated README.md: Custom kernel 6.17.13 section, version references

All Parrot/Debian branding removed. uname, /proc/version, and build
identity strings are NullSec-native (nullsec@nullsec.sh).

v5.0.0: Release infrastructure - DistroWatch submission, CI/CD, Calam…

…ares installer, checksums, 9 editions

v4.0.0 - NullSec Linux with 90+ tools

NullSec Linux v1.0.0 - Initial Release

Custom Linux distribution installer for security researchers.

Features:
- Automated NullSec tools installation
- System hardening configurations
- Security-focused package selection