test(documents): lock /incomplete size cap at 200

Regression test proving the controller clamps client-supplied size
values server-side, closing the unbounded-limit concern Markus flagged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -421,6 +421,17 @@ class DocumentControllerTest {
                 .andExpect(status().isForbidden());
     }
 
+    @Test
+    @WithMockUser(authorities = "WRITE_ALL")
+    void getIncomplete_capsSizeAt200() throws Exception {
+        when(documentService.findIncompleteDocuments(anyInt())).thenReturn(List.of());
+
+        mockMvc.perform(get("/api/documents/incomplete").param("size", "9999"))
+                .andExpect(status().isOk());
+
+        verify(documentService).findIncompleteDocuments(200);
+    }
+
     // ─── GET /api/documents/incomplete/next ──────────────────────────────────
 
     @Test