## Summary
- Fixes Argos CI builds showing as "Orphan" (no reference branch) for PR
builds
- Computes the merge-base SHA between the PR head and `main` using the
GitHub API (`compareCommitsWithBasehead`) in the dispatch workflow
- Passes `reference_commit` in the `ci-privileged` dispatch payload so
it can be forwarded to the Argos upload API
## Context
PR builds on Argos were showing as "Orphan" because `ci-privileged`
(where the actual Argos upload happens) has no git history of the
`twenty` repo — it cannot compute the merge-base locally. Without a
`referenceCommit`, Argos can't determine which `main` build to compare
against.
The local `visual-diff.sh` script already passes
`ARGOS_REFERENCE_COMMIT` via `git merge-base HEAD main`, but the CI
pipeline was missing this. This PR adds equivalent logic using the
GitHub API (no checkout needed).
## Note for ci-privileged
The `upload-to-argos.ts` script in `ci-privileged` needs a corresponding
update to read `reference_commit` from the dispatch payload and pass it
as `referenceCommit` in the Argos API call:
```typescript
referenceCommit: process.env.REFERENCE_COMMIT || undefined,
```
## Test plan
- [ ] Verify the workflow runs successfully on a PR (merge-base step
computes a SHA)
- [ ] Confirm Argos PR builds are no longer marked as "Orphan" after the
ci-privileged counterpart is updated
