add reminder rollup RPC and broker query

Surface reminder activity statistics (scheduled, delivered, pending counts)
for each agent over configurable time windows. Needed by the per-agent
stats page to display reminder metrics.

Adds:
- ReminderStats struct and ReminderRollup request/response variants
- Broker::reminder_rollup_for(agent, since_secs) method
- Agent and manager socket handlers for the new RPC
- SocketReply mapping for response conversion

hive-sh4re/src/lib.rs

@@ -110,6 +110,17 @@ pub enum ApprovalStatus {
     Failed,
 }
 
+/// Reminder activity statistics for an agent over a time window.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ReminderStats {
+    /// Total reminders scheduled in the window (created_at >= cutoff).
+    pub scheduled: u64,
+    /// Reminders that have been delivered in the window (sent_at IS NOT NULL).
+    pub delivered: u64,
+    /// Reminders still pending in the window (sent_at IS NULL).
+    pub pending: u64,
+}
+
 impl HostResponse {
     pub fn success() -> Self {
         Self {
@@ -381,6 +392,16 @@ pub enum AgentRequest {
     /// by the harness's per-turn stats sink to snapshot "what was
     /// queued at turn-end time" without paying for a full list.
     CountPendingReminders,
+    /// Reminder statistics for this agent: counts of scheduled, delivered,
+    /// and pending reminders over a time window. Used by the stats page
+    /// to display reminder activity. `since_secs` filters to reminders
+    /// created in the last N seconds (0 = all reminders).
+    ReminderRollup {
+        /// Only count reminders created in the last N seconds from now.
+        /// Pass 0 to include all reminders.
+        #[serde(default)]
+        since_secs: u64,
+    },
     /// Self-introspection: who am I, what role, what rev. All values
     /// derive from coord state (no env access required); useful for
     /// agents to stamp notes / commits / messages with a trustworthy
@@ -445,6 +466,8 @@ pub enum AgentResponse {
     LooseEnds { loose_ends: Vec<LooseEnd> },
     /// `CountPendingReminders` result.
     PendingRemindersCount { count: u64 },
+    /// `ReminderRollup` result: reminder activity stats for the agent.
+    ReminderRollup(ReminderStats),
     /// `Whoami` result: identity + role + the current hyperhive rev
     /// hive-c0re is running against. `role` is `"agent"` for
     /// sub-agents (the only path that reaches this variant of the
@@ -730,6 +753,14 @@ pub enum ManagerRequest {
     /// Count of the manager's own pending reminders. Mirror of
     /// `AgentRequest::CountPendingReminders` on the manager surface.
     CountPendingReminders,
+    /// Reminder statistics: counts of scheduled, delivered, and pending
+    /// reminders (manager-flavour). Mirror of `AgentRequest::ReminderRollup`.
+    ReminderRollup {
+        /// Only count reminders created in the last N seconds from now.
+        /// Pass 0 to include all reminders.
+        #[serde(default)]
+        since_secs: u64,
+    },
     /// Manager-flavour self-introspection. Same wire shape as
     /// `AgentRequest::Whoami`, but `role` is always `"manager"`.
     Whoami,
@@ -788,6 +819,8 @@ pub enum ManagerResponse {
     PendingRemindersCount {
         count: u64,
     },
+    /// `ReminderRollup` result: reminder activity stats for the manager.
+    ReminderRollup(ReminderStats),
     /// `Whoami` result: manager identity. `role` is always
     /// `"manager"`. Mirror of `AgentResponse::Whoami`.
     Whoami {