fix: support npm 12 pack output

[sarveshsea]

Summary

• normalize npm 10/11 array and npm 12 workspace-keyed pack JSON through one fail-closed parser
• use the parser in MCP packed proof, ten-package packed proof, and release artifact packing
• pin npm 12.0.1 in Node 24 CI while retaining complete packed-package coverage on Node 22

Root cause

Release run 29520812990 failed before publication because npm 12 changed workspace pack JSON from a one-element array to an object keyed by workspace name. No npm package, GitHub tag/release, or MCP Registry version was published.

Test plan

• npx --yes npm@12.0.1 run verify
• npx --yes npm@12.0.1 run test:mcp:packed
• npx --yes npm@12.0.1 run test:packages:packed
• npx --yes npm@12.0.1 run test:release-supply-chain
• npm run check:links:external
• npm run bench
• npm audit --audit-level=high

Code and security review: GO.

---

^{Need help on this PR? Tag /codesmith with what you need. Autofix is disabled.}