Support "control after generate" in vue (#6985)

Continuation of #6034 with
- Updated synchronization for seed
- Properly truncates the displayed widget value for the button
- Synchronizes control after generate state with litegraph and allows
for serialization

Several issues from original PR have not (yet) been addressed, but are
likely better moved to future PR
- fix step value being 10 (legacy system)
- ensure it works with COMBO (Fixed in #7095)
- ensure it works with FLOAT (Fixed in #7095)
- either implement or remove the config button functionality - think it
should open settings?

<img width="280" height="694" alt="image"
src="https://github.com/user-attachments/assets/f36f1cb0-237d-4bfc-bff1-e4976775cf98"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6985-Support-control-after-generate-in-vue-2b86d73d365081d8b01ce489d887ff00)
by [Unito](https://www.unito.io)

---------

Co-authored-by: bymyself <cbyrne@comfy.org>
Co-authored-by: github-actions <github-actions@github.com>

src/renderer/extensions/vueNodes/widgets/components/WidgetInputNumberSlider.vue

@@ -39,6 +39,7 @@ import {
   filterWidgetProps
 } from '@/utils/widgetPropFilter'
 
+import { useNumberStepCalculation } from '../composables/useNumberStepCalculation'
 import { useNumberWidgetButtonPt } from '../composables/useNumberWidgetButtonPt'
 import { WidgetInputBaseClass } from './layout'
 import WidgetLayoutField from './layout/WidgetLayoutField.vue'
@@ -56,7 +57,7 @@ const updateLocalValue = (newValue: number[] | undefined): void => {
 }
 
 const handleNumberInputUpdate = (newValue: number | undefined) => {
-  if (newValue) {
+  if (newValue !== undefined) {
     updateLocalValue([newValue])
     return
   }
@@ -67,33 +68,11 @@ const filteredProps = computed(() =>
   filterWidgetProps(widget.options, STANDARD_EXCLUDED_PROPS)
 )
 
-// Get the precision value for proper number formatting
-const precision = computed(() => {
-  const p = widget.options?.precision
-  // Treat negative or non-numeric precision as undefined
-  return typeof p === 'number' && p >= 0 ? p : undefined
-})
+const p = widget.options?.precision
+const precision = typeof p === 'number' && p >= 0 ? p : undefined
 
 // Calculate the step value based on precision or widget options
-const stepValue = computed(() => {
-  // Use step2 (correct input spec value) instead of step (legacy 10x value)
-  if (widget.options?.step2 !== undefined) {
-    return widget.options.step2
-  }
-
-  // Otherwise, derive from precision
-  if (precision.value === undefined) {
-    return undefined
-  }
-
-  if (precision.value === 0) {
-    return 1
-  }
-
-  // For precision > 0, step = 1 / (10^precision)
-  // precision 1 → 0.1, precision 2 → 0.01, etc.
-  return 1 / Math.pow(10, precision.value)
-})
+const stepValue = useNumberStepCalculation(widget.options, precision, true)
 
 const sliderNumberPt = useNumberWidgetButtonPt({
   roundedLeft: true,