fix: disable job asset actions when preview output is missing (#8700)

### Motivation
- Prevent context-menu actions from operating on stale or non-existent
assets when a completed job has no `previewOutput`, since `Inspect
asset`, `Add to current workflow`, and `Download` should be inactive in
that case.
- Also ensure the `Inspect asset` entry is disabled when the optional
inspect callback is not provided to avoid unexpected behavior.

### Description
- Added an optional `disabled?: boolean` field to the `MenuEntry` type
returned by `useJobMenu` and computed `hasPreviewAsset` to detect when
`taskRef.previewOutput` is present.
- Mark `inspect-asset`, `add-to-current`, and `download` entries as
`disabled` when the preview is missing (and also when the inspect
callback is missing for `inspect-asset`), and keep `delete` omitted when
no preview exists.
- Updated `JobContextMenu.vue` to pass `:disabled="entry.disabled"` to
the rendered `Button` and to short-circuit the action emit when an entry
is disabled.
- Expanded `useJobMenu` unit tests to assert enabled states when a
preview exists and disabled states when preview or inspect handler is
missing.

### Testing
- Ran `pnpm vitest src/composables/queue/useJobMenu.test.ts` and all
tests passed (36 tests).
- Ran `pnpm lint` and the linter reported no warnings or errors.
- Ran `pnpm typecheck` (`vue-tsc --noEmit`) and type checking completed
without errors.

------
[Codex
Task](https://chatgpt.com/codex/tasks/task_e_69864ed56e408330b88c3e9def1b5fb5)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8700-fix-disable-job-asset-actions-when-preview-output-is-missing-2ff6d73d365081b8b72ccadf0ae43e9d)
by [Unito](https://www.unito.io)

src/components/queue/job/JobContextMenu.test.ts

@@ -0,0 +1,81 @@
+import { mount } from '@vue/test-utils'
+import { describe, expect, it, vi } from 'vitest'
+
+import JobContextMenu from '@/components/queue/job/JobContextMenu.vue'
+import type { MenuEntry } from '@/composables/queue/useJobMenu'
+
+const buttonStub = {
+  props: {
+    disabled: {
+      type: Boolean,
+      default: false
+    }
+  },
+  template: `
+    <div
+      class="button-stub"
+      :data-disabled="String(disabled)"
+    >
+      <slot />
+    </div>
+  `
+}
+
+const createEntries = (): MenuEntry[] => [
+  { key: 'enabled', label: 'Enabled action', onClick: vi.fn() },
+  {
+    key: 'disabled',
+    label: 'Disabled action',
+    disabled: true,
+    onClick: vi.fn()
+  },
+  { kind: 'divider', key: 'divider-1' }
+]
+
+const mountComponent = (entries: MenuEntry[]) =>
+  mount(JobContextMenu, {
+    props: { entries },
+    global: {
+      stubs: {
+        Popover: {
+          template: '<div class="popover-stub"><slot /></div>'
+        },
+        Button: buttonStub
+      }
+    }
+  })
+
+describe('JobContextMenu', () => {
+  it('passes disabled state to action buttons', () => {
+    const wrapper = mountComponent(createEntries())
+
+    const buttons = wrapper.findAll('.button-stub')
+    expect(buttons).toHaveLength(2)
+    expect(buttons[0].attributes('data-disabled')).toBe('false')
+    expect(buttons[1].attributes('data-disabled')).toBe('true')
+  })
+
+  it('emits action for enabled entries', async () => {
+    const entries = createEntries()
+    const wrapper = mountComponent(entries)
+
+    await wrapper.findAll('.button-stub')[0].trigger('click')
+
+    expect(wrapper.emitted('action')).toEqual([[entries[0]]])
+  })
+
+  it('does not emit action for disabled entries', async () => {
+    const wrapper = mountComponent([
+      {
+        key: 'disabled',
+        label: 'Disabled action',
+        disabled: true,
+        onClick: vi.fn()
+      }
+    ])
+
+    await wrapper.get('.button-stub').trigger('click')
+
+    expect(wrapper.emitted('action')).toBeUndefined()
+  })
+})