Added callbacks for node errors and fifo overflow

Add new doc system which should/might deploy to pages.

include/kpn/network.hpp

@@ -44,6 +44,9 @@ public:
     using DiagnosticsHandler =
         std::function<void(const std::vector<NodeSnapshot>&,
                            const std::vector<ChannelSnapshot>&)>;
+    using EventHandler =
+        std::function<void(std::string_view node_name, NodeEvent,
+                           std::chrono::steady_clock::time_point)>;
 
     // ── Builder API ───────────────────────────────────────────────────────────
 
@@ -111,6 +114,19 @@ public:
         for (auto& [name, _] : nodes_)
             if (color[name] == 0)
                 dfs(name, color);
+        if (event_handler_) {
+            for (auto& name : topo_) {
+                auto* node = nodes_.at(name);
+                node->set_network_overflow_callback(
+                    [this, n = name](auto ts) {
+                        event_handler_(n, NodeEvent::Overflow, ts);
+                    });
+                node->set_network_closed_callback(
+                    [this, n = name](auto ts) {
+                        event_handler_(n, NodeEvent::Closed, ts);
+                    });
+            }
+        }
         return *this;
     }
 
@@ -194,8 +210,9 @@ public:
         watchdog_interval_ = interval;
     }
 
-    void set_error_handler(ErrorHandler h)       { error_handler_       = std::move(h); }
+    void set_error_handler(ErrorHandler h)             { error_handler_  = std::move(h); }
     void set_diagnostics_handler(DiagnosticsHandler h) { diag_handler_  = std::move(h); }
+    void set_event_handler(EventHandler h)             { event_handler_  = std::move(h); }
 
     void register_pool(const std::string& name, IPoolProbe* probe) {
         pool_probes_.emplace_back(name, probe);
@@ -430,6 +447,7 @@ private:
     std::vector<std::pair<std::string, IPoolProbe*>>       pool_probes_;
     ErrorHandler                                           error_handler_;
     DiagnosticsHandler                                     diag_handler_;
+    EventHandler                                           event_handler_;
     std::chrono::milliseconds                              watchdog_interval_{3000};
     std::jthread                                           watchdog_;
     clock_t::time_point                                    start_time_;