W17: extract ai_common shared module + fix anthropic data race + brace bugs

- New plugins_upper/ai_common/ static library: shared PluginConfig, ToolCallAccum,
  StreamContext, secure_zero, extract_host_port, serialize_tool_calls, free_chat_result
- Refactored openai/anthropic plugins to use dstalk_ai:: namespace from ai_common
- Fixed anthropic g_config raw pointer → std::atomic (data race)
- Added SSE parse error counter with threshold abort (kMaxSseParseErrors=5)
- Fixed missing closing brace in both plugins' error-body catch block
- Updated test targets: ai_common include path + link, using namespace dstalk_ai
- plugin_loader_test: added stub_unreg + service_registry.cpp for unregister_service
- Includes pre-existing uncommitted changes from prior waves

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins_middle/session/CMakeLists.txt

@@ -1,11 +1,11 @@
-add_library(plugin-session SHARED src/session_plugin.cpp)
+add_library(plugin_session SHARED src/session_plugin.cpp)
 
-target_link_libraries(plugin-session PRIVATE dstalk)
+target_link_libraries(plugin_session PRIVATE dstalk)
 
 find_package(Boost REQUIRED CONFIG)
-target_link_libraries(plugin-session PRIVATE boost::boost dstalk_boost_config)
+target_link_libraries(plugin_session PRIVATE boost::boost dstalk_boost_config)
 
-set_target_properties(plugin-session PROPERTIES
+set_target_properties(plugin_session PROPERTIES
     PREFIX ""
     LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/plugins"
     RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/plugins"

plugins_middle/session/src/session_plugin.cpp

@@ -5,7 +5,7 @@
  * Copyright (c) 2026 dstalk contributors. GPLv3.
  */
 
-// plugin-session: 会话管理服务插件 / Session management service plugin
+// plugin_session: 会话管理服务插件 / Session management service plugin
 // 提供 dstalk_session_service_t vtable 实现 / Provides dstalk_session_service_t vtable implementation
 // 依赖: file_io (save/load 需要文件操作) / Depends on: file_io (save/load needs file operations)
 #include "dstalk/dstalk_host.h"
@@ -356,7 +356,7 @@ static int on_init(const dstalk_host_api_t* host) {
         // 查询依赖服务: file_io / Query dependency service: file_io
         void* raw = host->query_service("file_io", 1);
         if (!raw) {
-            host->log(DSTALK_LOG_ERROR, "[plugin-session] required service 'file_io' not found");
+            host->log(DSTALK_LOG_ERROR, "[plugin_session] required service 'file_io' not found");
             return -1;
         }
         g_file_io.store(static_cast<const dstalk_file_io_service_t*>(raw), std::memory_order_release);