fix(model-pricing): refresh tiered expression editor when switching models (#5752)

Switching models in the pricing editor kept the previous model's tiers and prices in the expression panel: TieredPricingEditor seeds its internal visual/raw state only on mount, and the initRef guard never re-ran on prop changes, so only the model name updated.

Bump a reload token in the same effect that seeds billingExpr and use it as the editor's key, so a freshly loaded model remounts the editor and re-parses its expression. The token changes in lockstep with billingExpr, and user edits (which only touch state) do not trigger it.

Closes #5750

web/default/src/features/system-settings/models/model-pricing-sheet.tsx

@@ -153,6 +153,7 @@ export const ModelPricingEditorPanel = forwardRef<
   })
   const [billingExpr, setBillingExpr] = useState('')
   const [requestRuleExpr, setRequestRuleExpr] = useState('')
+  const [editorReloadToken, setEditorReloadToken] = useState(0)
   const isEditMode = !!editData
 
   const form = useForm<ModelPricingFormValues>({
@@ -214,6 +215,7 @@ export const ModelPricingEditorPanel = forwardRef<
     setPromptPrice(nextLaneState.promptPrice)
     setLanePrices(nextLaneState.prices)
     setLaneEnabled(nextLaneState.enabled)
+    setEditorReloadToken((token) => token + 1)
   }, [editData, form])
 
   const setFormValue = (field: keyof ModelPricingFormValues, value: string) => {
@@ -638,6 +640,7 @@ export const ModelPricingEditorPanel = forwardRef<
                   <TabsContent value='tiered_expr' className='pt-0'>
                     <FieldGroup className='gap-5'>
                       <TieredPricingEditor
+                        key={editorReloadToken}
                         modelName={watchedValues.name}
                         billingExpr={billingExpr}
                         requestRuleExpr={requestRuleExpr}