[WIP] Copilot cloud agent request

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Migrate the dependency 'zod' to 4.4.3 on a new branch and open ONE pull request titled 'chore(deps-major): migrate zod to 4.4.3 2026-06-24'. This is a KNOWN BREAKING major bump — work through the migration carefully using this assessment as the spec:

3→4 major. Actual code surface is modest (z.string().email() ×10 is deprecated-not-broken; z.record(z.any()) unaffected; no errorMap/.format()/.flatten() used; .parse() throw behavior unchanged across schemas in workers/lib/schemas.ts + workers/index.ts + agent/mcp). But it's the LYNCHPIN for the kumo v2 upgrade and requires removing the kumo zod override. Optional codemod z.string().email()→z.email(). Verify ai@^6 / agents@^0.7 against zod 4.

Apply the code changes the breaking changes require, run the project's install + test/build, and make sure it is green before opening the PR. Keep the change scoped to THIS migration only (do not bump unrelated dependencies, do not refactor). Do NOT merge.