fix(#2650,#2649): drop reminders tab + pending_reminders chip

hive-c0re's broker reminder store and /api/reminders endpoint were
removed in PR #2644 (reminders migrated to in-container sqlite store).
The dashboard had a QU3U3D R3M1ND3RS section on the schedules tab backed
by that endpoint, and a per-agent badge driven by pending_reminders
(always 0 after the migration).

Remove both. Per-agent reminders now surface through get_loose_ends /
the todos pill on the agent page, consistent with the todos migration.

- frontend/packages/dashboard/src/schedules.js: drop refreshReminders,
  renderReminders, applyRemindersChanged; drop appendLinkified import
  (no longer used); update module comment.
- frontend/packages/dashboard/src/tabs.js: drop applyRemindersChanged
  and refreshReminders imports; remove reminders-section from managed
  list; remove refreshReminders call site; drop reminders_changed from
  SSE dispatch; simplify countdown ticker (reminder-due gone).
- frontend/packages/dashboard/src/dashboard.html: remove QU3U3D
  R3M1ND3RS section.
- frontend/packages/dashboard/src/dashboard.css: remove reminder list +
  row CSS.
- frontend/packages/dashboard/src/common.css: remove .badge-reminder.
- frontend/packages/dashboard/src/swarm.js: remove pending_reminders
  from fingerprint key and badge render.

frontend/packages/dashboard/src/dashboard.css

@@ -675,42 +675,6 @@ summary:hover { color: var(--purple); }
   padding: 0.6em 0.9em;
   animation: questions-pulse 2.4s ease-in-out infinite;
 }
-.reminders {
-  list-style: none;
-  padding: 0;
-  margin: 0;
-}
-.reminder-row {
-  padding: 0.4em 0;
-  border-bottom: 1px solid var(--border);
-}
-.reminder-row:last-child { border-bottom: 0; }
-.reminder-head { font-size: 0.9em; }
-.reminder-body {
-  color: var(--fg);
-  white-space: pre-wrap;
-  word-break: break-word;
-  margin: 0.3em 0;
-}
-.reminder-row.reminder-failed {
-  border-left: 2px solid var(--red);
-  padding-left: 0.5em;
-}
-.reminder-error {
-  color: var(--red);
-  background: color-mix(in srgb, var(--red) 6%, transparent);
-  border: 1px solid color-mix(in srgb, var(--red) 25%, transparent);
-  padding: 0.3em 0.5em;
-  font-size: 0.85em;
-  white-space: pre-wrap;
-  word-break: break-word;
-  margin: 0.2em 0;
-}
-.reminder-actions {
-  display: flex;
-  gap: 0.4em;
-  margin-top: 0.3em;
-}
 
 .questions-filters {
   display: flex;