Update Nix flake for v0.1.2-pr-review and publish pre-release

[rowan-stein]

Update Nix flake for v0.1.2-pr-review and publish pre-release

Goal

• Publish a new pre-release v0.1.2-pr-review built from contrib/pr-review-commands (includes common resolver refactor).
• Update Nix branch feature/nix-flake to reference v0.1.2-pr-review, validate nix build/run/develop, and refresh README.

Tasks

1. Tag and publish v0.1.2-pr-review with cross-platform artifacts + SHA256SUMS.
2. Update Nix PR feat: add nix flake packaging #32 to mention v0.1.2-pr-review and validate Nix flows.

Notes

• Keep upstream-facing branch clean; no Nix files there.
• Release notes should highlight common resolver integration.