feat: add reset-to-default for widget parameters in right side panel (#8861)

## Summary

Add per-widget and reset-all-parameters functionality to the right side
panel, allowing users to quickly revert widget values to their defaults.

## Changes

- **What**: Per-widget "Reset to default" option in the WidgetActions
overflow menu, plus a "Reset all parameters" button in each
SectionWidgets header. Defaults are derived from the InputSpec (explicit
default, then type-specific fallbacks: 0 for INT/FLOAT, false for
BOOLEAN, empty string for STRING, first option for COMBO).
- **Dependencies**: Builds on #8594 (WidgetValueStore) for reactive UI
updates after reset.

## Review Focus

- `getWidgetDefaultValue` fallback logic in `src/utils/widgetUtil.ts` —
are the type-specific defaults appropriate?
- Deep equality check (`isEqual`) for disabling the reset button when
the value already matches the default.
- Event flow: WidgetActions emits `resetToDefault` → WidgetItem forwards
→ SectionWidgets handles via `writeWidgetValue` (sets value, triggers
callback, marks canvas dirty).

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8861-feat-add-reset-to-default-for-widget-parameters-in-right-side-panel-3076d73d365081d1aa08d5b965a16cf4)
by [Unito](https://www.unito.io)

Co-authored-by: Terry Jia <terryjia88@gmail.com>

src/utils/widgetUtil.ts

@@ -2,6 +2,32 @@ import { isProxyWidget } from '@/core/graph/subgraph/proxyWidget'
 import type { LGraphNode } from '@/lib/litegraph/src/LGraphNode'
 import type { SubgraphNode } from '@/lib/litegraph/src/subgraph/SubgraphNode'
 import type { IBaseWidget } from '@/lib/litegraph/src/types/widgets'
+import type { InputSpec } from '@/schemas/nodeDef/nodeDefSchemaV2'
+
+export type WidgetValue = boolean | number | string | object | undefined
+
+export function getWidgetDefaultValue(
+  spec: InputSpec | undefined
+): WidgetValue {
+  if (!spec) return undefined
+
+  if (spec.default !== undefined) return spec.default as WidgetValue
+
+  switch (spec.type) {
+    case 'INT':
+    case 'FLOAT':
+      return 0
+    case 'BOOLEAN':
+      return false
+    case 'STRING':
+      return ''
+    default:
+      if (Array.isArray(spec.options) && spec.options.length > 0) {
+        return spec.options[0] as WidgetValue
+      }
+      return undefined
+  }
+}
 
 /**
  * Renames a widget and its corresponding input.