Build Charts With Typed Params

Express the chart as typed, UI-shaped parameters and let the server compile it. Do not hand-build raw definition JSON.

Typed chart first

query_amplitude_data takes exactly one of chart or definition.

• chart (preferred) — a small model mirroring the chart builder UI. It is compiled server-side by Langley's CompileChart into a validated definition, so a successful compile is structurally correct by construction. Compile errors name the offending field and come back with a fix-oriented hint.
• definition (fallback) — raw definition JSON. Only for chart types the typed model does not cover (composition, revenueLtv) or advanced params with no typed field.

Field names are snake_case; they are validated server-side by Pydantic.