Evaluate Bazel/bzlmod for downstream consumers

[Jesssullivan]

Decision: Skip Bazel for now

Rationale

• zig-ctap2 is a pure Zig library — zig build is already hermetic and cacheable
• Bazel Zig rules (rules_zig) are immature/experimental
• Maintaining two build systems adds complexity for no current gain
• Nix flake provides reproducible builds + binary cache support (Attic)

Revisit criteria

• A downstream consumer (not cmux) needs Bazel integration
• rules_zig matures to support Zig 0.15+
• The library gains non-Zig dependencies