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.test.ts

@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest'
+
+import type { InputSpec } from '@/schemas/nodeDef/nodeDefSchemaV2'
+
+import { getWidgetDefaultValue } from '@/utils/widgetUtil'
+
+describe('getWidgetDefaultValue', () => {
+  it('returns undefined for undefined spec', () => {
+    expect(getWidgetDefaultValue(undefined)).toBeUndefined()
+  })
+
+  it('returns explicit default when provided', () => {
+    const spec = { type: 'INT', default: 42 } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBe(42)
+  })
+
+  it('returns 0 for INT type without default', () => {
+    const spec = { type: 'INT' } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBe(0)
+  })
+
+  it('returns 0 for FLOAT type without default', () => {
+    const spec = { type: 'FLOAT' } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBe(0)
+  })
+
+  it('returns false for BOOLEAN type without default', () => {
+    const spec = { type: 'BOOLEAN' } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBe(false)
+  })
+
+  it('returns empty string for STRING type without default', () => {
+    const spec = { type: 'STRING' } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBe('')
+  })
+
+  it('returns first option for array options without default', () => {
+    const spec = { type: 'COMBO', options: ['a', 'b', 'c'] } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBe('a')
+  })
+
+  it('returns undefined for unknown type without options', () => {
+    const spec = { type: 'CUSTOM' } as InputSpec
+    expect(getWidgetDefaultValue(spec)).toBeUndefined()
+  })
+})