fix: consistent error reporting + reset mapping modal per account

Error consistency: folder-level failures were counted only toward the task's
done_with_errors status, not the account's error_count, so a task showed
DONE_WITH_ERRORS while its only account showed 0 errors / DONE. Now folder
errors increment the account counter and the account status becomes
done_with_errors when errs>0.

Visibility: persist accounts.last_error (migration 0002) so the failing folder
/ login error survives a page reload (shown red under the source login);
cleared at the start of each run.

Modal reset: the folder-mapping modal kept its selections across opens, so
adding a second account showed the first account's mapping. It now mounts
fresh per add (conditional render + key), reflecting the newly-probed folders.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMHQTtnQtQqL8muAXHr9kd

web/src/pages/TaskDetail.tsx

@@ -473,7 +473,14 @@ export function TaskDetail({ id }: { id: number }) {
               ) : (
                 accounts.map((a) => (
                   <tr key={a.id}>
-                    <td>{a.src_login}</td>
+                    <td>
+                      {a.src_login}
+                      {a.last_error && (
+                        <div className="acct-error" title={a.last_error}>
+                          {a.last_error}
+                        </div>
+                      )}
+                    </td>
                     <td>{a.dst_login}</td>
                     <td>
                       <StatusBadge status={a.test_src_status} />
@@ -537,14 +544,17 @@ export function TaskDetail({ id }: { id: number }) {
         </div>
       </div>
 
-      <FolderMappingModal
-        open={mapState !== null}
-        srcFolders={mapState?.src ?? []}
-        dstFolders={mapState?.dst ?? []}
-        initialMapping={task.folder_mapping ?? {}}
-        onCancel={() => setMapState(null)}
-        onConfirm={confirmMapping}
-      />
+      {mapState && (
+        <FolderMappingModal
+          key={`${mapState.creds.src_login}|${mapState.creds.dst_login}`}
+          open
+          srcFolders={mapState.src}
+          dstFolders={mapState.dst}
+          initialMapping={task.folder_mapping ?? {}}
+          onCancel={() => setMapState(null)}
+          onConfirm={confirmMapping}
+        />
+      )}
     </>
   )
 }