Bump lastTag version to 0.17.2 (#2821)

## Summary
- Bump `lastTag` in `flake.nix` from 0.17.1 to 0.17.2
- Update `flake.lock` (nixpkgs 2026-04-14 → 2026-04-18)

## Test plan
- [x] `nix build .` succeeds
- [x] `./result/bin/devbox version` reports `0.17.2`

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Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>