Bump sha2 0.10 -> 0.11, update GHA actions, release 2026.4.2

Add license field to Cargo.toml, document nixpkgs upstream in CLAUDE.md

Update TLS dependencies to fix 3 security advisories

Add multi-arch Docker support (amd64 + arm64) via native GitHub Actions runners

Add alejandra to devShell buildInputs for CI compatibility

Major overhaul: security hardening, Nix-native Docker, expanded test matrix, CI pipeline

Merge pull request #35 from kittyandrew/dependabot/cargo/quinn-proto-0.11.14

Bump quinn-proto from 0.11.9 to 0.11.14

Bump bytes from 1.9.0 to 1.11.1

Bump actions/checkout from 5 to 6

Bump reqwest from 0.12.24 to 0.12.28

Bump reqwest from 0.12.22 to 0.12.24

Bump actions/checkout from 4 to 5

Bump tracing-subscriber from 0.3.19 to 0.3.20

Bump reqwest from 0.12.21 to 0.12.22