Chore/792 793 794 supply chain automation

[Cedarich]

Summary

• add weekly Dependabot updates for Cargo and GitHub Actions
• add CODEOWNERS coverage for the bridge, lending, and oracle contracts
• add CI validation to keep required CODEOWNERS entries in place
• add a release workflow that runs cargo deny check, generates propchain-sbom.json, validates it, and attaches it to releases
• document CODEOWNERS branch-protection requirements and SBOM interpretation

Verification

• cargo deny check

Follow-up

• enable GitHub branch protection on main with Require review from Code Owners

Closes #792
Closes #793
Closes #794

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