feat(audit): persistent audit log of agent-initiated privileged actions

Adds a durable, operator-visible audit trail of privileged operations
hive-c0re performs on behalf of an agent — the ones that cross the
agent/operator trust boundary. First entry: infra-container restarts via
the infra_admin-gated `restart` tool, which until now were recorded only
as a hive-priv journal trace.

Backend:
- new `audit_log` module: sqlite-backed store (audit_log.sqlite, same dir
  as build_logs) with schema (ts/agent/action/target/outcome/detail),
  best-effort `record`, `list_recent` (clamped 500), 90-day `vacuum`, and
  a process-singleton handle mirroring build_logs.
- Coordinator opens + installs the handle; main spawns the hourly vacuum.
- agent_server::handle_restart_infra records every attempt (ok, error, and
  capability-denied) via the global handle — best-effort, never fails the
  underlying action.
- dashboard: `GET /api/audit-log` returns recent entries as JSON.

Scope is deliberately agent-initiated privileged actions only (not every
PrivRequest — token writes + nspawn edits are constant lifecycle noise).
Extensible: future agent-initiated priv ops record via the same handle.

Unit tests cover record/list ordering, the 500 clamp, and retention vacuum.

The dashboard *surface* (an AUDIT view consuming /api/audit-log) is a
frontend follow-up coordinated with iris.

hive-c0re/src/dashboard.rs

@@ -104,6 +104,7 @@ pub async fn serve(port: u16, coord: Arc<Coordinator>) -> Result<()> {
         .route("/api/operator-inbox", get(api_operator_inbox))
         .route("/api/stats-hive", get(api_stats_hive))
         .route("/api/container-resources", get(api_container_resources))
+        .route("/api/audit-log", get(api_audit_log))
         .route("/api/build-logs", get(build_logs::get_build_logs_all))
         .route(
             "/api/build-logs/{agent}",
@@ -1312,6 +1313,16 @@ async fn api_container_resources() -> Response {
     axum::Json(crate::container_stats::gather().await).into_response()
 }
 
+/// `GET /api/audit-log` — most-recent agent-initiated privileged-action
+/// audit entries, newest first (server-clamped to 500). Backs the
+/// operator dashboard's audit view. Returns `Vec<AuditEntry>` JSON.
+async fn api_audit_log(State(state): State<AppState>) -> Response {
+    match state.coord.audit_log.list_recent(500) {
+        Ok(rows) => axum::Json(rows).into_response(),
+        Err(e) => error_response(&format!("audit-log: {e:#}")),
+    }
+}
+
 /// Validate that a path-param agent name conforms to the hyperhive
 /// naming whitelist: 1-63 chars of `[a-z0-9_-]`. Rejects empty,
 /// uppercase, slashes, dots, and any non-ASCII (incl. unicode