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>

backend/AGENTS.md

@@ -70,6 +70,7 @@ We use the karpathy-guidelines skill to reduce common LLM coding mistakes:
 2. **Simplicity First**: Write the minimum amount of code to solve the problem with zero speculative configurations.
 3. **Surgical Changes**: Edit only what is required and match the existing coding style exactly.
 4. **Goal-Driven Execution**: Define verifiable success criteria and run automated tests/screenshots to confirm correctness.
+5. **SOLID Principles**: Always design, implement, and refactor code adhering to SOLID programming principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) to ensure modularity, scalability, and maintainability.
 
 ## Path Guidelines (always follow)