feat(app): scan-mode sync, confirmation-gated documents, single-pass product classification

Fixes reported from APK field testing: DO/Product scan mode was inconsistent
between the camera drawer and documents screen (now one shared provider,
with an orange/green color cue); unconfirmed scans leaked into history with
placeholder data before the user tapped confirm (backend now gates
GET /documents on a new `confirmed` column, flipped only by PUT); and
Product Scan ran the GPU classifier twice, once at upload and again on
review (now a single pass at upload, persisted and read directly by the
editor). Also removes the unused "Hubungkan ke PO" field and fabricated
PO/SO/DO placeholder values from the Product Scan flow, closes out the
per-document-polling and save-recovery tasks (6.1/6.3), and splits several
touched files to stay under the repo's 256-line guideline.

Full detail in docs/iteration-log.md and backend/docs/iteration-log.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

test/camera_settings_test.dart

@@ -14,10 +14,10 @@ void main() {
     );
 
     // Verify Title exists
-    expect(find.text('OCR Document Scanner'), findsOneWidget);
+    expect(find.text('Pemindai Dokumen OCR'), findsOneWidget);
 
     // Verify main card header exists
-    expect(find.text('Pindai Dokumen DO'), findsOneWidget);
+    expect(find.text('Pemindai DO'), findsOneWidget);
 
     // Verify Camera button exists
     expect(find.text('Ambil Foto Kamera'), findsOneWidget);