fix(import): address non-blocking review feedback — touch target, glossary, edge-case test

- Add min-h-[44px] py-2 to <summary> in ImportStatusCard for 44 px touch target
- Add SkippedFile and skipped count entries to docs/GLOSSARY.md
- Add MassImportServiceTest case: ALREADY_EXISTS fires before file I/O when doc is UPLOADED and file is present on disk

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

backend/src/test/java/org/raddatz/familienarchiv/importing/MassImportServiceTest.java

@@ -160,6 +160,33 @@ class MassImportServiceTest {
         assertThat(result).isPresent().contains("ALREADY_EXISTS");
     }
 
+    // ─── importSingleDocument — already-exists guard fires before file I/O ─────
+
+    @Test
+    void importSingleDocument_skipsWithAlreadyExists_whenDocumentUploadedAndFileIsPresent(@TempDir Path tempDir) throws Exception {
+        // Document already exists with status UPLOADED (not PLACEHOLDER).
+        // A physical PDF file is also present on disk (valid magic bytes).
+        // Expected: ALREADY_EXISTS is returned and no S3 upload is attempted —
+        // the guard fires before any file I/O, so no partial processing occurs.
+        Document existing = Document.builder()
+                .id(UUID.randomUUID())
+                .originalFilename("present.pdf")
+                .status(DocumentStatus.UPLOADED)
+                .build();
+        when(documentService.findByOriginalFilename("present.pdf")).thenReturn(Optional.of(existing));
+
+        Path physicalFile = tempDir.resolve("present.pdf");
+        byte[] pdfHeader = {0x25, 0x50, 0x44, 0x46, 0x2D}; // %PDF-
+        Files.write(physicalFile, pdfHeader);
+
+        Optional<String> result = service.importSingleDocument(
+                minimalCells("present.pdf"), Optional.of(physicalFile.toFile()), "present.pdf", "present");
+
+        assertThat(result).isPresent().contains("ALREADY_EXISTS");
+        verify(s3Client, never()).putObject(any(PutObjectRequest.class), any(RequestBody.class));
+        verify(documentService, never()).save(any());
+    }
+
     // ─── importSingleDocument — S3 failure surfaced in skippedFiles ──────────
 
     @Test