The AI Toolkit examples call ai-api.ag-grid.com directly, which browsers block
from localhost on CORS (the upstream gates on an origin allow-list). Add a
dev-server-only Vite proxy at /ai-proxy that forwards upstream and can present
an allowed Origin/Referer and dev token server-side, both env-gated and inert
by default. Point an example's AI_API_URL at /ai-proxy via .env.local to use it.
This is dev tooling, separable from the example fix, and never ships in the
production static build.

showValuesAs was wired into ColumnState (getColumnState/applyColumnState) when
the feature landed, but never into the GridState projection, so getState/setState
silently dropped it. Carry it through AggregationColumnState, convertColumnState,
orderAggregationModel and the setState apply path so it round-trips like aggFunc.

Add a null schema builder (s.null) and extend the aggregation feature schema so
each aggregatable column exposes showValuesAs (built-in modes + null to clear)
when showValuesAsSvc is present. Behavioural tests cover the schema shape and the
full grid-state round-trip.

- Derive SHOW_VALUES_AS_BUILT_IN_TYPES from Record<ShowValuesAsBuiltInType, true>
  so the built-in mode set is compile-time coupled to the source union (typos,
  removals and additions now break the build instead of silently misinforming the LLM).
- Add a system-prompt note in both examples to carry over a column's existing
  showValuesAs on aggregation edits, since it is a required, nullable schema property.
- Cover the graceful-degradation branch: assert showValuesAs is omitted from the
  schema when ShowValuesAsModule is absent.

- Build the calculated-column ColDef by dropping the operation discriminator and
  unset values, instead of field-by-field conditional assignment.
- Keep the ChatToolPanel change minimal: add applyColumnDefOperations above the
  existing state-apply branch rather than restructuring the render/setState flow.