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/document_sync_merge.dart

@@ -0,0 +1,33 @@
+import '../../models/document_model.dart';
+
+/// Result of merging the server's document list with local corrections that
+/// haven't made it back to the server yet.
+class MergedDocuments {
+  final List<DocumentModel> docs;
+  final Set<String> unsyncedIds;
+
+  const MergedDocuments(this.docs, this.unsyncedIds);
+}
+
+/// Merges the server's authoritative document list with local corrections for
+/// documents whose `PUT` sync failed (`syncFailed` in the pending queue).
+///
+/// Without this, refreshing the documents list would silently overwrite a
+/// driver's corrected-but-unsynced edit with the server's stale pre-edit copy
+/// on every successful fetch - the correction is still recoverable via the
+/// pending queue's retry action, but the history list would show the wrong
+/// data (or the document would vanish from it entirely) until the retry
+/// succeeds. `unsyncedOverrides` wins over `serverDocs` for matching ids, and
+/// is kept even if the server list doesn't (yet) include that id at all.
+MergedDocuments mergeDocumentsWithUnsyncedOverrides({
+  required List<DocumentModel> serverDocs,
+  required Map<String, DocumentModel> unsyncedOverrides,
+}) {
+  final merged = <String, DocumentModel>{
+    for (final doc in serverDocs) doc.id: doc,
+  };
+  for (final entry in unsyncedOverrides.entries) {
+    merged[entry.key] = entry.value;
+  }
+  return MergedDocuments(merged.values.toList(), unsyncedOverrides.keys.toSet());
+}