Fix renderer-coupled notebook mutations

[jlewi]

Summary

This PR fixes the getAllRenderersRef notebook mutation bug by removing renderer hooks from notebook mutation paths and tightening insert behavior so failed patching does not leave partially inserted cells behind.

Changes

• add and refine the design doc for the getAllRenderersRef bug
• remove renderer callbacks from code-mode notebook mutation in ChatKitPanel
• make Actions.updateCellLocal(...) a model-only mutation path
• stop terminal seeding during mutation by making the legacy renderer hook a no-op
• rollback inserted cells when a later insert patch step fails
• add focused tests for local mutation behavior and insert rollback

Testing

• pnpm -C app exec vitest run src/components/Actions/Actions.test.tsx src/lib/runtime/runmeConsole.test.ts src/lib/runtime/codeModeExecutor.test.ts

Notes

• App-wide tsc -p tsconfig.app.json --noEmit is already failing on unrelated baseline issues in this branch and was not made worse by this change.
• Broader Actions.tsx / output-rendering follow-on work remains tracked in Refactor Actions.tsx output rendering and terminal-state handling #190.

[jlewi]

ubuntu-latest failure is an unrelated CI failure