Add supply-chain hardened .npmrc (PER-8331)

[pranavz28]

Supply-chain hardening: add .npmrc

Flagged by the weekly supply-chain .npmrc audit (PER-8331, parent SC-12282) with status missing_file.

Adds an .npmrc with the required hardening directives: ignore-scripts, strict-ssl, save-exact, audit-level=high, engine-strict, legacy-peer-deps=false. Public repo, so access=restricted is intentionally omitted (private-repo only).

⚠️ Reviewers: confirm CI npm install still passes — ignore-scripts/engine-strict/legacy-peer-deps can change install behavior.

Ref: Supply Chain Security Enhancements Tech Spec

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[ninadbstack]

Supply-chain hardening .npmrc (npmrc_audit / SC-12282)