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.html

@@ -206,19 +206,6 @@
         <p class="meta">loading…</p>
       </div>
 
-      <!-- QU3U3D R3M1ND3RS: self-scheduled agent reminders. Lives
-           on this tab so the operator has one place for everything
-           that fires at a future time — operator-set schedules
-           above, agent-self reminders here. Backed by GET
-           /api/reminders; live updates via `reminders_changed` SSE;
-           refreshReminders() called from refreshState + tab
-           activation as safety net for disconnect windows. -->
-      <h2>◆ QU3U3D R3M1ND3RS ◆</h2>
-      <div class="divider">══════════════════════════════════════════════════════════════</div>
-      <p class="meta">reminders agents have queued for themselves but not yet delivered. cancel to drop a stuck or unwanted entry.</p>
-      <div id="reminders-section">
-        <p class="meta">loading…</p>
-      </div>
     </section>
 
     <!-- ST4TS: hive-wide turn-stats aggregate lives on its own page now