chore(cla): pre-seed maintainer signature to break initial catch-22

[millerjp]

Summary

Pre-populates signatures/version1/cla.json with the maintainer's signature so the CLA Assistant flow can bootstrap. Without this, the repo maintainer cannot open their own first post-#18 PR (the CLA bot would block it; the bot's signing commit needs the maintainer to have already signed).

Shape

Matches the CLA Assistant wire format verbatim (same shape as axonops/mask's signatures/version1/cla.json):

```json
{
"signedContributors": [
{
"name": "Johnny Miller",
"id": 163300,
"comment_id": 0,
"created_at": "2026-04-21T07:30:00Z",
"repoId": 1215690488,
"pullRequestNo": 0,
"login": "millerjp"
}
]
}
```

Any future signature the bot records simply appends another object to `signedContributors` — no schema drift.

Secondary change

Regenerated `CONTRIBUTORS.md` via `scripts/generate-contributors.sh` so the `TestGovernance_ContributorsFileIsGenerated` byte-equality guard stays green.

Merge instructions

The CLA Assistant workflow (from #18) triggered on this PR will want you to sign — but you will need to bypass it for this one PR as an admin, because:

1. The workflow cannot fire successfully until `CLA_ASSISTANT_PAT` exists in repo secrets (its first successful run would also write to this file, conflicting with this PR's own diff).
2. The whole point of this PR is to pre-record your signature so the bot doesn't have to.

Squash-merge with admin override. The next PR you open after this one will then see you as already-signed and the CLA Assistant flow will pass cleanly — no admin bypass needed thereafter.

Post-merge:

• Create the `CLA_ASSISTANT_PAT` repo secret (classic PAT, `repo` scope, from an admin account).
• Open a throwaway test PR from a fork to confirm the bot behaves correctly for external contributors.

Test plan

• `make check` green locally
• `TestGovernance_ContributorsFileIsGenerated` passes (proves CONTRIBUTORS.md matches generator output exactly)
• `TestGovernance_SignaturesFileIsValid` passes (proves the JSON is valid and carries the expected key)
• Squash-merge via admin bypass

[github-actions]

Thank you for your contribution! Before we can merge this PR, you need to sign our Contributor License Agreement.

To sign, post a comment on this PR containing exactly:

I have read the CLA Document and I hereby sign the CLA

The CLA is a one-time agreement that covers every future contribution you make to any AxonOps open-source project. If you have questions before signing, please open a discussion or email oss@axonops.com.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}