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/documents/poll_outcome.dart

@@ -0,0 +1,39 @@
+import '../../models/document_model.dart';
+
+enum PollOutcomeKind { done, failed, pending }
+
+/// Result of inspecting a single `GET /documents/:id` poll response.
+/// Deliberately separated from the Dio call site
+/// (`pending_documents_provider.dart`'s `_pollUntilParsed`) so the
+/// parse-status branching is unit-testable without mocking network I/O -
+/// mirrors the pure-function pattern already used for `document_sync_merge.dart`
+/// (task 6.2) and `product_scan_response_parser.dart` (task 7.1).
+class PollOutcome {
+  final PollOutcomeKind kind;
+  final DocumentModel? document;
+  final String? message;
+
+  const PollOutcome._(this.kind, {this.document, this.message});
+
+  factory PollOutcome.done(DocumentModel document) =>
+      PollOutcome._(PollOutcomeKind.done, document: document);
+
+  factory PollOutcome.failed(String message) =>
+      PollOutcome._(PollOutcomeKind.failed, message: message);
+
+  static const PollOutcome pending = PollOutcome._(PollOutcomeKind.pending);
+}
+
+/// `parseStatus` absent/unrecognized (a legacy/cached response predating
+/// backend task 9.1) is treated the same as `"pending"` - keep polling rather
+/// than surface a false failure.
+PollOutcome resolvePollOutcome(DocumentModel fetched) {
+  switch (fetched.parseStatus) {
+    case 'done':
+      return PollOutcome.done(fetched);
+    case 'failed':
+      return PollOutcome.failed('Gagal mengekstrak data (parsing gagal di server).');
+    default:
+      return PollOutcome.pending;
+  }
+}