[AI Improvement] [Task] Upgrade nyc devDependency from ^15 to ^18

[joehan]

Resolves Buganizer b/567662388
Parent Goal: b/567660818

Proposed Improvement

Upgrades the nyc devDependency from ^15.1.0 to ^18.0.0.

• Resolves moderate npm audit vulnerability GHSA-w5hq-g745-h8pq (istanbul-lib-processinfo -> uuid <11.1.1).
• Confirms the existing package.json "nyc" configuration remains fully compatible with nyc@18 (reporters, include/exclude, extension, ts-node register).
• Lockfile (npm-shrinkwrap.json) was regenerated under Node 24 and normalized with CI's npm@11.9 (npx -y npm@11.9 install --package-lock-only --ignore-scripts).

Verification

• npm run build: Passed cleanly.
• npm run lint:quiet: Passed cleanly across the entire repository.
• npm run test:compile: Full type check passed without errors.
• npm run test:management: Passed 99/99 tests and generated complete coverage reports with nyc.
• npm audit: Verified that nyc, istanbul-lib-processinfo, and uuid are no longer flagged.

[gemini-code-assist]

Code Review

This pull request updates the nyc dependency in package.json from version ^15.1.0 to ^18.0.0. There are no review comments, so I have no feedback to provide.