feat: flag accounts Reddit considers unestablished and re-test them

New accounts cannot start chats until Reddit considers them established.
Until now the bot would burn a candidate on every invitation Reddit was
always going to reject, with nothing in the dashboard explaining why the
account looked idle.

Two signals feed the verdict. A periodic profile check reads the
account's own age, karma and email verification from about.json and
compares them against configurable thresholds — that is what flags a
brand new account before it wastes anything. A rejected invitation is
authoritative: Reddit has told us directly, so the account is held out of
sending with a backoff that doubles per rejection, and a delivered
invitation clears the flag outright.

An unestablished account takes no new posts (canAcceptPost), raises an
attention item, reports an `unestablished` sending state, and shows its
age/karma evidence on the Accounts page. An unchecked account is always
allowed through, so a first run is never blocked.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/dashboard/src/features/attention/attention-page.tsx

@@ -18,6 +18,8 @@ function actionHint(kind: AttentionItem['kind']): string {
   switch (kind) {
     case 'account-login-required':
       return 'No linked conversation — check Settings.';
+    case 'account-unestablished':
+      return 'No linked conversation — check Accounts.';
     case 'runtime-failed':
     case 'invitation-cooldown':
     default: