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>

lib/features/editor/pdf_service.dart

@@ -10,7 +10,7 @@ class PdfService {
     
     // Load PFM logo asset
     final logoImage = await flutterImageProvider(const AssetImage('assets/logo.png'));
-    final isProductScan = document.orderUntuk == 'PRODUCT SCAN';
+    final isProductScan = document.docType == 'Product';
     
     // Add page
     pdf.addPage(