chore: add supply chain hardening defaults

[joelhooks]

Summary

• Adds supply-chain hardening defaults for Shai-Hulud / worms-ctrl-style npm and CI attacks.
• Adds CODEOWNERS, GitHub-Actions-only Dependabot, advisory dependency review, advisory CodeQL, and supply-chain policy.
• Avoids package manager/lockfile churn.

Validation

• YAML parsed locally.
• pnpm typecheck passed locally.

Created after ShitRat-authored hardening commit.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: bcea85e9-21dd-41d0-9a57-e27ce8d866d7

📥 Commits

Reviewing files that changed from the base of the PR and between 914759b and 7d04870.

📒 Files selected for processing (5)

• .github/CODEOWNERS
• .github/dependabot.yml
• .github/workflows/codeql.yml
• .github/workflows/dependency-review.yml
• SECURITY_SUPPLY_CHAIN.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch shitrat/supply-chain-hardening

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