feat: add OpenAI-compatible AI provider plugin with SSE streaming support

- Implemented the OpenAI-compatible AI provider plugin, including configuration, chat, and chat_stream functionalities.
- Added support for SSE streaming and tool calls.
- Integrated Boost.JSON for JSON handling.
- Created CMake configuration for the plugin.
- Added error handling and logging throughout the plugin.

dstalk_core/src/event_bus.hpp

@@ -0,0 +1,50 @@
+/* @file event_bus.hpp
+ * @brief Publish-subscribe event bus with shared_mutex for concurrent read access.
+ * 发布-订阅事件总线，使用 shared_mutex 支持并发读访问。
+ * Copyright (c) 2026 dstalk contributors. GPLv3.
+ */
+
+#pragma once
+
+#include <functional>
+#include <mutex>
+#include <shared_mutex>
+#include <unordered_map>
+#include <vector>
+
+namespace dstalk {
+
+using EventHandler = std::function<void(int event_type, const void* data)>;
+
+// 轻量级发布-订阅事件总线 / Lightweight pub-sub event bus.
+// 读取者使用 shared_lock（emit），因此多个处理器可以并发分发；
+// 写入者使用 unique_lock（subscribe / unsubscribe）。
+// Readers use shared_lock (emit) so multiple handlers can be dispatched
+// concurrently; writers use unique_lock (subscribe / unsubscribe).
+class EventBus {
+public:
+    EventBus() = default;
+    ~EventBus() = default;
+
+    // 订阅事件，返回订阅ID / Subscribe to an event, returning a subscription id
+    int subscribe(int event_type, EventHandler handler);
+
+    // 取消订阅 / Unsubscribe by subscription id
+    void unsubscribe(int subscription_id);
+
+    // 发布事件 / Emit an event to all matching subscribers
+    int emit(int event_type, const void* data);
+
+private:
+    struct Subscription {
+        int id;
+        int event_type;
+        EventHandler handler;
+    };
+
+    mutable std::shared_mutex mutex_;             // 读写锁：emit 用 shared，subscribe/unsubscribe 用 unique / RW lock: shared for emit, unique for subscribe/unsubscribe
+    std::vector<Subscription> subscriptions_;     // emit 时线性扫描；对少量订阅者足够 / Linear scan on emit; ok for small subscriber counts
+    int next_id_ = 1;                             // 单调递增订阅 ID 计数器 / Monotonic subscription id counter
+};
+
+} // namespace dstalk