feat(quick-upload): generate better title from structured filename

titleFromFilename() mirrors the same four patterns as the frontend
parseFilename() utility. Dropzone uploads to Mueller_Hans_19650312.pdf
now land with title "Hans Mueller (12.03.1965)" instead of the raw
stripped filename.

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

backend/src/test/java/org/raddatz/familienarchiv/service/DocumentServiceTest.java

@@ -518,4 +518,40 @@ class DocumentServiceTest {
 
         assertThat(count).isEqualTo(2);
     }
+
+    // ─── titleFromFilename ────────────────────────────────────────────────────
+
+    @Test
+    void titleFromFilename_dateIso_name() {
+        assertThat(DocumentService.titleFromFilename("1965-03-12_Mueller_Hans.pdf"))
+                .isEqualTo("Hans Mueller (12.03.1965)");
+    }
+
+    @Test
+    void titleFromFilename_dateCompact_name() {
+        assertThat(DocumentService.titleFromFilename("19650312_Mueller_Hans.pdf"))
+                .isEqualTo("Hans Mueller (12.03.1965)");
+    }
+
+    @Test
+    void titleFromFilename_name_dateIso() {
+        assertThat(DocumentService.titleFromFilename("Mueller_Hans_1965-03-12.pdf"))
+                .isEqualTo("Hans Mueller (12.03.1965)");
+    }
+
+    @Test
+    void titleFromFilename_name_dateCompact() {
+        assertThat(DocumentService.titleFromFilename("Mueller_Hans_19650312.pdf"))
+                .isEqualTo("Hans Mueller (12.03.1965)");
+    }
+
+    @Test
+    void titleFromFilename_fallsBackToStripExtension() {
+        assertThat(DocumentService.titleFromFilename("scan_001.pdf")).isEqualTo("scan_001");
+    }
+
+    @Test
+    void titleFromFilename_null_returnsNull() {
+        assertThat(DocumentService.titleFromFilename(null)).isNull();
+    }
 }