[self-care:open-source-failures] Repair dependabot target authority for live-mode Release Trains

Recurring live-mode Dependabot Release Trains runs in `githubnext/gh-aw-cao` are blocked before activation because CAO precompute cannot find valid target authority for package `dependabot`. The bounded snapshot shows repeated failures with the same pre-activation step and one stricter validation error naming the missing authority field, so this is the second-highest ROI fix.

**Action:** `githubnext/gh-aw-cao` maintainers should add or repair `target-authority.packages.dependabot.authority` in `.github/workflows/cao.json` on the default branch; accept when a new live-mode Dependabot Release Trains run completes pre-activation without the target-authority error.

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Update `.github/workflows/cao.json` on the default branch so the target authority declaration is valid for package `dependabot` in live mode. Preserve existing rollout policy, add or repair `version: 1` and `target-authority.packages.dependabot.authority` as required by CAO, validate the JSON, and describe the minimal fix in the PR. Acceptance: rerun the Dependabot Release Trains workflow and confirm CAO control precompute no longer fails with a target-authority error.

- Severity: `P1`
- Repository: `githubnext/gh-aw-cao`
- Affected workflow: `.github/workflows/dependabot-release-train-updater.lock.yml`
- Normalized signature: `pre_activation / Run CAO control precompute / target authority missing for dependabot live mode`
- Probable cause: missing or incomplete target authority entry for `dependabot` in target `.github/workflows/cao.json`
- Confidence: `high`
- Representative runs:
- https://github.com/githubnext/gh-aw-cao/actions/runs/33947168768
- https://github.com/githubnext/gh-aw-cao/actions/runs/33947159838
- https://github.com/githubnext/gh-aw-cao/actions/runs/33947149703

Evidence

Representative failure messages observed in the bounded snapshot:
- `Target authority missing: add .github/workflows/cao.json to the target default branch for live mode`
- `Target authority file must declare version 1 and target-authority.packages.dependabot.authority`

Corroborating runs in the same cluster occurred repeatedly between `2026-09-05T05:25:02Z` and `2026-09-05T05:25:34Z`.

### Control Plane
- Correlation ID: `33949930283-204`
- Central repository: `githubnext/gh-aw-cao`
- Control-plane run: https://github.com/githubnext/gh-aw-cao/actions/runs/33949930283

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Start with .github/workflows/cao.json and compare its target-authority declaration with the validation errors for the dependabot package. Validate the JSON, then rerun .github/workflows/dependabot-release-train-updater.lock.yml; the fix is done when live-mode pre-activation completes without a target-authority error.

Written by the indexing model from the issue text.