Fix/licence drift - #37

Adds `open-pull-requests-limit` to Dependabot update blocks that had no
cap, following the estate per-ecosystem cap doctrine (task #37). No
other line in the file is touched.


Claude-Session: https://claude.ai/code/session_011eQ7hibx92N7fBDtwgReWk

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SPDX-License-Identifier: CC-BY-SA-4.0
Copyright (c) Jonathan D.A. Jewell <[email protected]>
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## Summary

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with "Closes #N". -->

## Changes

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-

## RSR Quality Checklist

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merged. -->

### Required

- [ ] Tests pass (`just test` or equivalent)
- [ ] Code is formatted (`just fmt` or equivalent)
- [ ] Linter is clean (no new warnings or errors)
- [ ] No banned language patterns (no TypeScript, no npm/bun, no
Go/Python)
- [ ] No `unsafe` blocks without `// SAFETY:` comments
- [ ] No banned functions (`believe_me`, `unsafeCoerce`, `Obj.magic`,
`Admitted`, `sorry`)
- [ ] SPDX license headers present on all new/modified source files
- [ ] No secrets, credentials, or `.env` files included

### As Applicable

- [ ] `.machine_readable/STATE.a2ml` updated (if project state changed)
- [ ] `.machine_readable/ECOSYSTEM.a2ml` updated (if integrations
changed)
- [ ] `.machine_readable/META.a2ml` updated (if architectural decisions
changed)
- [ ] Documentation updated for user-facing changes
- [ ] `TOPOLOGY.md` updated (if architecture changed)
- [ ] `CHANGELOG` or release notes updated
- [ ] New dependencies reviewed for license compatibility
(PMPL-1.0-or-later / MPL-2.0)
- [ ] ABI/FFI changes validated (`src/interface/abi/` and
`src/interface/ffi/` consistent)

## Testing

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## Screenshots

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change. -->

Co-authored-by: Claude Opus 5 <[email protected]>