fix(server): Omit null fields in control JSON editor

[lan17]

Summary

This updates the control JSON editor so null object fields are not rendered in Full JSON mode.

What changed

• Added a recursive UI-side normalizer that removes object properties whose values are null
• Used that normalized shape when seeding the edit-control modal state
• Used null-free stringification when switching from form mode to Full JSON mode
• Added a regression test covering a composite condition tree with nullable transport fields

Why

Controls are not persisted with these null keys in the database, but the UI was rendering the nullable transport shape returned by the API. That made Full JSON mode noisy with entries like "or": null and "selector": null.

Validation

• pnpm exec eslint src/core/page-components/agent-detail/modals/edit-control/edit-control-content.tsx src/core/page-components/agent-detail/modals/edit-control/utils.ts tests/agent-detail.spec.ts

Notes

• Full Playwright verification is currently blocked locally by unrelated UI environment issues, including a missing motion/react module when starting a fresh dev server.
• make ui-typecheck also currently fails elsewhere in the UI for unrelated type errors.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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