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/common.css

@@ -77,10 +77,6 @@ code {
   color: var(--muted); border-color: var(--purple-dim);
   background: color-mix(in srgb, var(--muted) 8%, transparent);
 }
-.badge-reminder {
-  color: var(--cyan); border-color: var(--cyan);
-  text-shadow: 0 0 6px color-mix(in srgb, var(--cyan) 40%, transparent);
-}
 .badge-loose-ends {
   color: var(--purple); border-color: var(--purple);
   text-shadow: 0 0 6px color-mix(in srgb, var(--purple) 40%, transparent);