docs: overhaul docs IA and multilingual navigation

docs/contributing/README.md

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+# Contributing, Review, and CI Docs
+
+For contributors, reviewers, and maintainers.
+
+## Core Policies
+
+- Contribution guide: [../../CONTRIBUTING.md](../../CONTRIBUTING.md)
+- PR workflow rules: [../pr-workflow.md](../pr-workflow.md)
+- Reviewer playbook: [../reviewer-playbook.md](../reviewer-playbook.md)
+- CI map and ownership: [../ci-map.md](../ci-map.md)
+- Actions source policy: [../actions-source-policy.md](../actions-source-policy.md)
+
+## Suggested Reading Order
+
+1. `CONTRIBUTING.md`
+2. `docs/pr-workflow.md`
+3. `docs/reviewer-playbook.md`
+4. `docs/ci-map.md`