feat: detect and resolve duplicate correspondents in Agrarmonitor sync

- Detect duplicates after sync (same AgrarmonitorId, multiple correspondents)
- Auto-merge duplicates with identical names (delete empty, move docs to larger)
- Expose conflicts with different names for manual resolution
- New mergeCorrespondents endpoint + service method
- Conflict resolution modal in SettingsPage with radio selection per conflict
- deleteCorrespondent added to PaperlessService

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

paperless-frontend/src/api/settings.ts

@@ -210,6 +210,19 @@ export interface AgrarmonitorPollingResult {
   errors: string[];
 }
 
+export interface SyncConflict {
+  agrarmonitorId: number;
+  correspondents: Array<{ id: number; name: string; documentCount: number }>;
+}
+
+export interface SyncCorrespondentsResult {
+  total: number;
+  matched: number;
+  unmatched: number;
+  autoMerged: number;
+  conflicts: SyncConflict[];
+}
+
 export const agrarmonitorApi = {
   getStatus: () =>
     api.get<AgrarmonitorStatusData>('/api/agrarmonitor/status').then((r) => r.data),
@@ -226,5 +239,7 @@ export const agrarmonitorApi = {
   processUploads: () =>
     api.post<AgrarmonitorPollingResult>('/api/agrarmonitor/process-uploads').then((r) => r.data),
   syncCorrespondents: () =>
-    api.post<{ total: number; matched: number; unmatched: number }>('/api/agrarmonitor/sync-correspondents').then((r) => r.data),
+    api.post<SyncCorrespondentsResult>('/api/agrarmonitor/sync-correspondents').then((r) => r.data),
+  mergeCorrespondents: (keepId: number, deleteId: number) =>
+    api.post<{ mergedDocuments: number }>('/api/agrarmonitor/merge-correspondents', { keepId, deleteId }).then((r) => r.data),
 };