chore(renovate): track openclaw + remote-signer helm chart pins

[bussyjd]

Summary

• Add a customManager (regex) that parses the existing // renovate: hint comments in internal/openclaw/openclaw.go, so Renovate actually tracks both helm pins:
  • chartVersion = \"0.1.7\" (openclaw chart on https://obolnetwork.github.io/helm-charts/)
  • remoteSignerChartVersion = \"0.3.0\" (remote-signer chart)
    The hint comments were already present but there was no matching manager — they were dead labels.
• Add package rules mirroring the existing obol-stack-front-end style: grouped PRs with a nice body template for remote-signer, grouped PRs for the openclaw chart, and a major-bump gate via the dependency dashboard for remote-signer.

Regex verification

The regex was test-compiled against the current source and matches both pins exactly:

```
datasource=helm depName=openclaw registryUrl=https://obolnetwork.github.io/helm-charts/ currentValue=0.1.7
datasource=helm depName=remote-signer registryUrl=https://obolnetwork.github.io/helm-charts/ currentValue=0.3.0
```

Expected effect on next Renovate run

Pin	Now	Latest	PR?
`remoteSignerChartVersion`	0.3.0	0.3.0	no (already current)
openclaw chart `chartVersion`	0.1.7	0.4.0	yes — major bump (covered by a separate openclaw bump PR)
Frontend (unchanged, already tracked)	v0.1.16	v0.1.16	no

Test plan

• JSON schema valid
• Regex matches both pins in `openclaw.go` locally
• Renovate dry-run picks up the new manager on next scheduled run
• First PR Renovate opens for a helm chart update is labeled/grouped as expected