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.css

@@ -4,8 +4,8 @@
 
 /* SYST3M panel rules (rebuild queue / meta inputs / container load)
    live in system-sections.css, shared with /core.html. A few are still
-   referenced from dashboard JS (the schedules view uses `.rqe-source*`),
-   so the dashboard pulls them in here. */
+   referenced from the dashboard (`.rebuild-queue`), so the dashboard
+   pulls them in here. */
 @import "./system-sections.css";
 @import "@hive/shared/jobq-rollup.css";
 
@@ -709,113 +709,6 @@ footer .banner-thin {
   cursor: not-allowed;
 }
 
-/* ─── scheduled prompts tab ────────────────────────────────────────
-   Read-only table of the schedules left in the hive's store. */
-
-.schedules-table-wrap {
-  overflow-x: auto;
-  margin-top: 0.5em;
-}
-.schedules-table {
-  min-width: 100%;
-  border-collapse: collapse;
-  font-size: 0.82em;
-}
-.schedules-table th,
-.schedules-table td {
-  padding: 0.35em 0.6em;
-  border: 1px solid var(--border);
-  vertical-align: middle;
-}
-.schedules-table thead th {
-  background: var(--bg-elev);
-  color: var(--muted);
-  font-weight: normal;
-  text-transform: uppercase;
-  letter-spacing: 0.05em;
-  white-space: nowrap;
-}
-.schedules-table-id {
-  width: 3em;
-  text-align: center;
-}
-.schedules-table-next-col {
-  white-space: nowrap;
-}
-/* every column: sized to typical content (short durations). */
-.schedules-table-every-col {
-  width: 5em;
-  white-space: nowrap;
-}
-.schedules-table-body-th {
-  min-width: 12em;
-}
-/* Agent-name columns: 90° vertical text (writing-mode) so names are fully
-   readable without truncation. Previously used a -45° CSS transform which
-   clipped names mid-glyph. writing-mode + rotate(180deg) is in-flow and
-   needs no absolute positioning or overflow hacks. */
-.schedules-table-agent-th {
-  width: 28px;
-  min-width: 28px;
-  height: 8em;
-  padding: 4px 2px !important;
-  vertical-align: bottom;
-  text-transform: none !important;
-  letter-spacing: 0 !important;
-  overflow: hidden;
-}
-.schedules-table-agent-th > div {
-  font-family: ui-monospace, "JetBrains Mono", monospace;
-  font-size: 0.85em;
-  color: var(--fg);
-  /* Rotate 90° bottom-to-top (conventional rotated column header). */
-  writing-mode: vertical-rl;
-  transform: rotate(180deg);
-  white-space: nowrap;
-  overflow: hidden;
-  text-overflow: ellipsis;
-  max-height: 7.5em;
-}
-.schedules-table-agent-th > div > span {
-  display: inline-block;
-  padding: 0 2px;
-}
-/* Column for an agent no longer in the live roster — its past schedules
-   linger but the agent is gone. Greyed + struck through. */
-.schedules-table-agent-th--gone > div {
-  color: var(--muted);
-  text-decoration: line-through;
-  opacity: 0.75;
-}
-.schedules-table-row-cancelled td {
-  opacity: 0.55;
-}
-.schedules-table-row-paused td {
-  opacity: 0.75;
-}
-.sched-paused-label {
-  color: var(--yellow);
-  font-size: 0.9em;
-}
-.schedules-table-body-cell {
-  max-width: 30em;
-  overflow: hidden;
-  text-overflow: ellipsis;
-  white-space: nowrap;
-  font-family: ui-monospace, "JetBrains Mono", monospace;
-  font-size: 0.9em;
-}
-.schedules-table-check {
-  width: 28px;
-  text-align: center;
-  color: var(--green);
-  padding: 0.3em 0 !important;
-}
-.schedules-table-check-cancelled {
-  color: var(--muted);
-  font-size: 0.9em;
-}
-
 /* Selection bar — sticky-bottom strip for bulk actions. */
 .selection-bar {
   position: fixed;