refactor(layout): extract canUpload derived for the upload-button gate (#696)

Move the inline {#if data?.user && data.canWrite} condition into a named
$derived, matching the existing isAdmin / isAuthPage derivations in the
same file. No behaviour change — the 11 layout specs stay green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/document/DocumentControllerTest.java

@@ -297,6 +297,13 @@ class DocumentControllerTest {
                 .andExpect(status().isForbidden());
     }
 
+    @Test
+    @WithMockUser(authorities = "READ_ALL")
+    void createDocument_returns403_forReaderOnly() throws Exception {
+        mockMvc.perform(multipart("/api/documents").with(csrf()))
+                .andExpect(status().isForbidden());
+    }
+
     @Test
     @WithMockUser(authorities = "WRITE_ALL")
     void createDocument_returns200_whenHasWritePermission() throws Exception {
@@ -414,6 +421,13 @@ class DocumentControllerTest {
                 .andExpect(status().isForbidden());
     }
 
+    @Test
+    @WithMockUser(authorities = "READ_ALL")
+    void quickUpload_returns403_forReaderOnly() throws Exception {
+        mockMvc.perform(multipart("/api/documents/quick-upload").with(csrf()))
+                .andExpect(status().isForbidden());
+    }
+
     @Test
     @WithMockUser(authorities = "WRITE_ALL")
     void quickUpload_returns200_withValidPdfFile() throws Exception {

frontend/src/routes/+layout.svelte

@@ -43,6 +43,8 @@ const isAdmin = $derived(
 	data?.user?.groups?.some((g: { permissions: string[] }) => g.permissions.includes('ADMIN'))
 );
 
+const canUpload = $derived(Boolean(data?.user && data.canWrite));
+
 // Set after client-side hydration completes. Used by E2E tests to know the
 // page is interactive (event handlers registered) before they interact with it.
 let hydrated = $state(false);
@@ -75,7 +77,7 @@ const userInitials = $derived.by(() => {
 
 					<!-- Right Side -->
 					<div class="flex items-center gap-3">
-						{#if data?.user}
+						{#if canUpload}
 							<a
 								href="/documents/new"
 								aria-label={m.upload_action()}

frontend/src/routes/layout.svelte.spec.ts

@@ -83,6 +83,23 @@ describe('Layout – upload link', () => {
 		const link = page.getByRole('link', { name: /Hochladen|Upload|Subir/i });
 		await expect.element(link).toHaveAttribute('href', '/documents/new');
 	});
+
+	it('is hidden for a user without WRITE_ALL', async () => {
+		render(Layout, { data: makeData({ canWrite: false }), children: emptySnippet });
+		await expect
+			.element(page.getByRole('link', { name: /Hochladen|Upload|Subir/i }))
+			.not.toBeInTheDocument();
+	});
+
+	it('is hidden for an ANNOTATE_ALL-only user (gate is lack of WRITE_ALL, not READ_ALL)', async () => {
+		render(Layout, {
+			data: makeData({ canWrite: false, canAnnotate: true }),
+			children: emptySnippet
+		});
+		await expect
+			.element(page.getByRole('link', { name: /Hochladen|Upload|Subir/i }))
+			.not.toBeInTheDocument();
+	});
 });
 
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