fix(genie): dispatchAlignmentStep still uses nix run nixpkgs#gh instead of plain gh

Problem

dispatchAlignmentStep in genie/ci-workflow.ts uses nix run nixpkgs#gh to invoke the GitHub CLI. The notify-alignment job runs on ubuntu-latest (GitHub-hosted runners) which do not have Nix installed, causing every run to fail with:

/usr/bin/bash: line 1: nix: command not found

This has broken the notify-alignment job in downstream repos (e.g. livestore) on every push to dev since ~March 8, 2026.

Root cause

The fix was implemented in #417 (March 20) but then reverted in #422 (March 22) when lightweight jobs were moved to self-hosted runners. It was supposedly fixed again in #443 (March 23), but examining the file content at main HEAD (ad96132d) shows it still has the nix run version.

Possible solutions

Option A: Use pre-installed gh directly

gh is pre-installed on all GitHub-hosted runners. Remove the Nix wrapper entirely:

run: [
  `printf '{"event_type":"${opts.eventType ?? 'upstream-changed'}","client_payload":{"source_repo":"%s","source_sha":"%s"}}'`,
  `  "${'${{ github.repository }}'}" "${'${{ github.sha }}'}"`,
  `| gh api repos/${opts.targetRepo}/dispatches --input -`,
].join(' \\\n'),

Option B: Move notify-alignment to a self-hosted runner with Nix

If the intent from #422 was to run all lightweight jobs on self-hosted runners (where Nix is available), then notifyAlignmentJob should use a self-hosted runner config instead of ubuntu-latest. The current runs-on: ubuntu-latest contradicts the nix run usage.

Start in genie/ci-workflow.ts at dispatchAlignmentStep and inspect how notifyAlignmentJob sets its runner and invokes gh. Compare the current ubuntu-latest configuration with the two proposed approaches, then verify that the generated job no longer depends on an unavailable command or runner assumption.