forms(qml): SlotRegistry has no tier by renderer kind, so a host cannot restyle every Quantity / Choice / enum / date-time control at once

[Yaraslaut]

Verification: inferred from reading SlotRegistry.qml and DynamicForm.qml on master 05222af; not measured with a host app.

SlotRegistry.resolve(action, field, xWidget, unitAscii, jsonType) resolves by field, x-widget, unit and JSON type. The JSON type does not identify the control a host needs to supply:

Member	jsonType passed	Also matched by the same byType
Quantity<U, Dec>	"object" (["object","null"])	every nested aggregate, every Choice over an object
Choice<std::int64_t, …>	"integer"	every plain integral member
enum class (closed set)	"string"	every text field
Timestamp (format: date-time)	"string"	every text field

So a host whose visuals must all come from its own UI kit (one combo component, one date picker, one quantity entry) has to register byField per action and field, or byUnit per unit. DynamicForm already classifies every field (isQuantity, isChoice, isEnum, isDateTime, isBoolean, isInteger, isNumber, isArray, isObjectArray after #809, isMultiline, isSlider, isRadioChoice).

Proposal: a byKind(kind, component) tier between unit and type, with kind derived from those flags ("quantity", "choice", "enum", "datetime", "boolean", "integer", "number", "array", "objectArray", "text", …) and put on the field descriptor. Not folded into #809/#810 because it changes resolve()'s signature, which both touch.

Closes when a host can register one component per control kind and every field of that kind resolves to it.