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/composables/useNumberStepCalculation.ts

@@ -0,0 +1,35 @@
+import { computed, toValue } from 'vue'
+import type { MaybeRefOrGetter } from 'vue'
+
+interface NumberWidgetOptions {
+  step2?: number
+  precision?: number
+}
+
+/**
+ * Shared composable for calculating step values in number input widgets
+ * Handles both explicit step2 values and precision-derived steps
+ */
+export function useNumberStepCalculation(
+  options: NumberWidgetOptions | undefined,
+  precisionArg: MaybeRefOrGetter<number | undefined>,
+  returnUndefinedForDefault = false
+) {
+  return computed(() => {
+    const precision = toValue(precisionArg)
+    // Use step2 (correct input spec value) instead of step (legacy 10x value)
+    if (options?.step2 !== undefined) {
+      return Number(options.step2)
+    }
+
+    if (precision === undefined) {
+      return returnUndefinedForDefault ? undefined : 0
+    }
+
+    if (precision === 0) return 1
+
+    // For precision > 0, step = 1 / (10^precision)
+    const step = 1 / Math.pow(10, precision)
+    return returnUndefinedForDefault ? step : Number(step.toFixed(precision))
+  })
+}