turn_stats: per-turn analytics sink

new sqlite table at /state/hyperhive-turn-stats.sqlite on each
agent's state dir. one row per claude turn captures identity
(model, wake_from, result_kind), timing (started/ended_at,
duration_ms), cost (input/output/cache_read/cache_creation token
counts), behaviour (tool_call_count + per-tool breakdown JSON),
and post-turn snapshot metrics (open_threads_count,
open_reminders_count).

wire additions:
- AgentRequest/ManagerRequest::CountPendingReminders +
  Broker::count_pending_reminders_for(agent)
- Bus::observe_stream + take_tool_calls — pumps the existing
  stdout stream-json, picks out tool_use blocks, accumulates per
  turn. bin loops fold the breakdown into each row.
- TurnStats::open_default + TurnStatRow + record() — best-effort
  inserts; failures log + don't block the harness.

both ag3nt and m1nd bins capture started_at + duration via
Instant::elapsed, fetch open-thread + reminder counts from
hive-c0re via the existing socket (post-turn, best-effort), and
record one row at turn_end. record_kind splits ok / failed /
prompt_too_long; failures carry the error message in note.

todo entries for host-side vacuum sweep + reading the table back
into agent/dashboard badges.

hive-sh4re/src/lib.rs

@@ -309,6 +309,10 @@ pub enum AgentRequest {
     /// manager); questions surface where the agent is `asker` or
     /// `target`. Cheap O(n) sweep server-side — no caching.
     GetOpenThreads,
+    /// Count of this agent's pending (un-delivered) reminders. Used
+    /// by the harness's per-turn stats sink to snapshot "what was
+    /// queued at turn-end time" without paying for a full list.
+    CountPendingReminders,
 }
 
 /// Responses on a per-agent socket.
@@ -333,6 +337,8 @@ pub enum AgentResponse {
     /// `GetOpenThreads` result: list of loose ends pending against
     /// this agent. Ordered newest-first within each kind.
     OpenThreads { threads: Vec<OpenThread> },
+    /// `CountPendingReminders` result.
+    PendingRemindersCount { count: u64 },
 }
 
 // -----------------------------------------------------------------------------
@@ -596,6 +602,9 @@ pub enum ManagerRequest {
     /// sub-agent surface is `AgentRequest::GetOpenThreads` which
     /// only returns rows where the agent itself is asker / target.
     GetOpenThreads,
+    /// Count of the manager's own pending reminders. Mirror of
+    /// `AgentRequest::CountPendingReminders` on the manager surface.
+    CountPendingReminders,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -634,4 +643,8 @@ pub enum ManagerResponse {
     OpenThreads {
         threads: Vec<OpenThread>,
     },
+    /// `CountPendingReminders` result.
+    PendingRemindersCount {
+        count: u64,
+    },
 }