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>

AGENTS.md

@@ -122,8 +122,9 @@ no clear "done" condition). If so:
     (memory/CPU) assumptions per `SKILLS.md`.
 - In your final response, state which task(s) were completed and the exact menu/navigation path to see the new feature.
 
-## 3. File Size & Refactoring Rules
+## 3. File Size, Refactoring & SOLID Rules
 
+- **SOLID Principles**: Always design, implement, and refactor code adhering to SOLID programming principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion). This ensures code is modular, testable, and maintainable.
 - **256-line threshold**: any code/script file — new, modified, or pre-existing —
   that exceeds 256 lines of code must be split into smaller, modular, logical files.
   This is a repo-wide rule, not just for new work; if you touch a file over the
@@ -190,9 +191,12 @@ Recorded 2026-07-08, from adopting this kit into the existing `app-pfm-ocr-v2` r
   only if/when touched going forward), **Flutter only** now that `backend/` is out of
   scope for this kit (see §Scope above; backend's own debt list, re-verified
   2026-07-08, lives in `backend/AGENTS.md`'s Adaptation Notes instead):
-  `lib/features/editor/editor_screen.dart` (682), `lib/features/documents/documents_screen.dart`
-  (442), `lib/features/camera/image_preview_screen.dart` (380), `lib/features/camera/camera_screen.dart`
-  (376), `lib/features/documents/pending_documents_provider.dart` (271).
+  `lib/features/camera/image_preview_screen.dart` (380), `lib/features/camera/camera_screen.dart`
+  (376). (`editor_screen.dart` was split 2026-07-10 when task 6.3 touched it —
+  see root `plans/next-enhancements.md` §6.3 and `docs/iteration-log.md`;
+  `documents_screen.dart` and `pending_documents_provider.dart` were already
+  split down by earlier iterations and are no longer over threshold — this
+  line was stale.)
 - **No Demo/Live or Cloud/Local switch exists yet** (§5, §6). The closest existing
   analogue is `AppConfig.initializeApiBaseUrl()` in `lib/config/app_config.dart`,
   which dynamically resolves a *real* backend endpoint (ngrok tunnel, falling back to