Allow artworks to have one primary category and extra secondaries.

Keep artwork_category as membership, store a deterministic primary_category_id, and let upload plus studio pick up to five additional same-type categories without changing canonical URLs.

resources/js/components/upload/__tests__/UploadWizard.test.jsx

@@ -347,6 +347,30 @@ describe('UploadWizard step flow', () => {
     expect(window.axios.post).not.toHaveBeenCalledWith('/api/uploads/session-1/publish', expect.anything(), expect.anything())
   })
 
+  it('shows additional categories alphabetically after the primary path is chosen', async () => {
+    installAxiosStubs({ statusValue: 'ready' })
+    await renderWizard({
+      initialDraftId: 318,
+      contentTypes: [{
+        id: 1,
+        name: 'Art',
+        categories: [
+          { id: 10, name: 'Root', children: [{ id: 11, name: 'Sub' }, { id: 14, name: 'Zebra' }] },
+          { id: 12, name: 'Apple', children: [{ id: 13, name: 'City' }] },
+        ],
+      }],
+    })
+
+    await completeStep1ToReady()
+    expect(await screen.findByText(/artwork details/i)).not.toBeNull()
+    await completeRequiredDetails({ title: 'My Art' })
+
+    const extraHeading = await screen.findByText(/additional categories/i)
+    const extraSection = extraHeading.closest('div')?.parentElement
+    const extraNames = Array.from(extraSection?.querySelectorAll('button') || []).map((button) => button.textContent?.trim())
+    expect(extraNames).toEqual(['Apple', 'City', 'Root', 'Zebra'])
+  })
+
   it('hides the mature content checkbox in the details step', async () => {
     installAxiosStubs({ statusValue: 'ready' })
     await renderWizard({ initialDraftId: 311, contentTypes: [{ id: 1, name: 'Art', categories: [{ id: 10, name: 'Root', children: [{ id: 11, name: 'Sub' }] }] }] })