feat(errors): per-account error modal with persisted error list

Accounts finishing done_with_errors showed only a count and a single
last_error. This adds a modal listing every concrete error of the
account's most recent run.

- migration 0005: account_errors table (kind folder|message|account,
  folder, message_ref, error, created_at; ON DELETE CASCADE; indexed)
- store: AddAccountError / ClearAccountErrors / ListAccountErrors
- copy: OnError callback captures per-message error text (previously
  only counted), with a "UID N: subject" reference
- orchestrator: clear errors at run start; persist folder/message/
  account errors; cap 500 rows/account/run with a suppressed-note row
- api: GET /api/tasks/{id}/accounts/{accountId}/errors
- web: AccountErrorsModal, clickable ERRORS count, api + styles

Verified: migration applies on Postgres 18; store add/list/clear and
cascade tests pass against real pg; backend build/vet/test green; web
tsc+vite build and oxlint clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U9Eq4JtWjyNTv5qat3B3mM

web/src/pages/TaskDetail.tsx

@@ -5,6 +5,7 @@ import { StatusBadge } from '../components/StatusBadge'
 import { useConfirm } from '../components/ConfirmProvider'
 import { FolderMappingModal } from '../components/FolderMappingModal'
 import { RunLogModal } from '../components/RunLogModal'
+import { AccountErrorsModal } from '../components/AccountErrorsModal'
 
 const emptyAccount = { src_login: '', src_pass: '', dst_login: '', dst_pass: '' }
 
@@ -87,6 +88,7 @@ export function TaskDetail({ id }: { id: number }) {
   const [error, setError] = useState<string | null>(null)
   const [live, setLive] = useState<Record<number, LiveProgress>>({})
   const [showRuns, setShowRuns] = useState(false)
+  const [errorsFor, setErrorsFor] = useState<{ id: number; src_login: string } | null>(null)
   const fileInputRef = useRef<HTMLInputElement>(null)
 
   function reload() {
@@ -609,7 +611,19 @@ export function TaskDetail({ id }: { id: number }) {
                     </td>
                     <td className="num-cell">{live[a.id]?.copied ?? a.copied}</td>
                     <td className="num-cell">{live[a.id]?.skipped ?? a.skipped}</td>
-                    <td className="num-cell">{a.errors}</td>
+                    <td className="num-cell">
+                      {a.errors > 0 ? (
+                        <button
+                          type="button"
+                          className="link-btn danger"
+                          onClick={() => setErrorsFor({ id: a.id, src_login: a.src_login })}
+                        >
+                          {a.errors}
+                        </button>
+                      ) : (
+                        a.errors
+                      )}
+                    </td>
                     <td className="num-cell">
                       <div className="row-actions">
                         {a.status !== 'running' && data?.task.status !== 'running' && (
@@ -671,6 +685,7 @@ export function TaskDetail({ id }: { id: number }) {
         />
       )}
       <RunLogModal taskId={id} open={showRuns} onClose={() => setShowRuns(false)} />
+      <AccountErrorsModal taskId={id} account={errorsFor} onClose={() => setErrorsFor(null)} />
     </>
   )
 }