dashboard: queued reminders surface

new 'qu3u3d r3m1nd3rs' section between approvals and operator
inbox. lists every pending reminder with agent, due-relative
timestamp, body, payload path (path-linkified), and a cancel
button. drives off a new /api/reminders endpoint and a
POST /cancel-reminder/{id} that hard-deletes the row.

failure surface (last_error / attempt_count + retry) deferred —
needs a sqlite migration; tracked in TODO.md.

hive-c0re/src/broker.rs

@@ -46,6 +46,19 @@ const EVENT_CHANNEL: usize = 256;
 /// self-documenting.
 pub type DueReminder = (String, i64, String, Option<String>);
 
+/// Row shape for [`Broker::list_pending_reminders`], shipped on the
+/// dashboard `/api/reminders` response.
+#[derive(Debug, Clone, Serialize)]
+pub struct PendingReminder {
+    pub id: i64,
+    pub agent: String,
+    pub message: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub file_path: Option<String>,
+    pub due_at: i64,
+    pub created_at: i64,
+}
+
 /// Intra-process broker event. `recv_blocking` listens on the same
 /// channel as the dashboard forwarder; the forwarder re-emits each
 /// event as a `DashboardEvent` with a freshly-stamped seq from the
@@ -286,6 +299,44 @@ impl Broker {
         Ok(id)
     }
 
+    /// Every reminder still pending delivery, newest-first. Used by the
+    /// dashboard's reminders pane so the operator can see what's queued
+    /// + cancel rows that are no longer wanted.
+    pub fn list_pending_reminders(&self) -> Result<Vec<PendingReminder>> {
+        let conn = self.conn.lock().unwrap();
+        let mut stmt = conn.prepare(
+            "SELECT id, agent, message, file_path, due_at, created_at \
+               FROM reminders \
+              WHERE sent_at IS NULL \
+              ORDER BY due_at ASC",
+        )?;
+        let rows = stmt.query_map([], |row| {
+            Ok(PendingReminder {
+                id: row.get(0)?,
+                agent: row.get(1)?,
+                message: row.get(2)?,
+                file_path: row.get(3)?,
+                due_at: row.get(4)?,
+                created_at: row.get(5)?,
+            })
+        })?;
+        rows.collect::<rusqlite::Result<Vec<_>>>()
+            .context("list pending reminders")
+    }
+
+    /// Delete a reminder by id. Returns the number of rows removed (0
+    /// when the id never existed or was already delivered). Hard
+    /// delete rather than soft so the row doesn't linger and confuse a
+    /// re-creation under the same id.
+    pub fn cancel_reminder(&self, id: i64) -> Result<usize> {
+        let conn = self.conn.lock().unwrap();
+        let n = conn.execute(
+            "DELETE FROM reminders WHERE id = ?1 AND sent_at IS NULL",
+            params![id],
+        )?;
+        Ok(n)
+    }
+
     /// Get up to `limit` due reminders across all agents in a single query.
     /// Returns `(agent, id, message, file_path)` tuples. Pass a small limit
     /// (e.g. 100) so a burst of overdue reminders doesn't flood the broker