hive: remove the read-only schedules page and the old schedule store

Scheduled prompts live at swarm level (swarm-controller's
/api/schedules, `swarmctl schedule`, the swarm UI's /schedules page).
The hive dashboard's SCH3DUL3S tab only listed the rows left in
hive-c0re's `scheduled_prompts` table so operators could copy them
over; the operator confirmed everything is migrated.

Removed:
- the SCH3DUL3S tab, its pane, schedules.js, its CSS (including the
  `.rqe-source*` rules, whose only emitter was schedules.js) and the
  hub tile's "schedules" entry
- hive-c0re's GET /api/schedules and the `scheduled_prompts` store
  (with its v1 column migration and test)
- hive-sh4re's `schedule` wire types, which only that route used
- docs describing the tab, the route and the two tables

The rebuild-queue cancel route that shared the module moves to
dashboard/rebuild_queue.rs under an OpenAPI tag of its own.

The two sqlite tables are not dropped: nothing opens them any more,
and persistence.md says they can be dropped by hand.

Closes #4916

frontend/packages/dashboard/src/dashboard.html

@@ -53,21 +53,6 @@
           <span class="tab-label">◆ P3RM1SS10NS ◆</span>
         </a>
 
-        <!-- SCH3DUL3S: read-only scheduled-prompts list. Count pill
-           mirrors the active (non-cancelled) schedule count; hidden
-           when zero. -->
-        <a
-          class="tab"
-          id="tab-schedules"
-          href="#schedules"
-          role="tab"
-          aria-controls="tab-pane-schedules"
-          data-tab="schedules"
-        >
-          <span class="tab-label">◆ SCH3DUL3S ◆</span>
-          <span class="tab-count" id="tab-count-schedules" hidden></span>
-        </a>
-
         <!-- ST4TS lives on its own page now (`/stats.html`), reached from
            the H0M3 hub — the hive-wide rollup is a standalone read-only
            view, not part of the operational tab strip. -->
@@ -190,38 +175,6 @@
           </div>
         </section>
 
-        <!-- SCH3DUL3S: read-only list of the scheduled prompts left in the
-         hive's store, driven by GET /api/schedules (re-fetched on tab
-         activation). Nothing on the hive fires them; the banner points
-         at `swarmctl schedule`, where schedules live now.
-         See docs/web-ui/dashboard.md::SCH3DUL3S tab. -->
-        <section
-          class="tab-pane"
-          id="tab-pane-schedules"
-          data-tab-pane="schedules"
-          hidden
-          role="tabpanel"
-          aria-labelledby="tab-schedules"
-        >
-          <h2>◆ SCH3DUL3S ◆</h2>
-          <div class="divider">
-            ══════════════════════════════════════════════════════════════
-          </div>
-          <p class="server-warn server-warn-warn" role="note">
-            ⚠ this page is slated for removal. the hive no longer fires these
-            schedules — they live at swarm level now: recreate each one with
-            <code>swarmctl schedule add</code> (see
-            <code>docs/swarm/schedules.md</code>).
-          </p>
-          <p class="meta">
-            read-only: every schedule still in the hive's table, kept so it can
-            be copied over.
-          </p>
-          <div id="schedules-section">
-            <p class="meta">loading…</p>
-          </div>
-        </section>
-
         <!-- ST4TS: hive-wide turn-stats aggregate lives on its own page now
          (`/stats.html`), reached from the H0M3 hub. The markup + the
          hive-stats render JS moved there; when tabs.js boots on the