refactor(messaging): 拆分用户交互模块到 application/messaging 层

- 新增 application/messaging 交互层：router.py 统一会话优先级与回调分发，
  site/subscribe/skill/media/plugin 各交互状态与视图从 Chain 迁出
- MessageChain 改为通过 InteractionRouter 派发文本会话与按钮回调，
  新增结构化 callback_data 通道（兼容 CALLBACK: 文本前缀）
- Transfer 失败重试/AI 接管回调归入 TransferChain
- MediaInteractionChain 拆出为 app/chain/interaction.py（旧路径保留兼容别名）
- WebAgent Endpoint 去重，统一使用 agent.py 回调协议函数
- 删除 app/chain/skills.py（交互逻辑并入 SkillInteractionHandler）
- 同步更新架构文档与测试，全量 4476 通过

tests/test_slash_command_interactions.py

@@ -11,21 +11,22 @@ ensure_optional_stub("aioshutil")
 ensure_optional_stub("pyquery", PyQuery=object)
 
 from app.chain.message import MessageChain
+from app.application.messaging.interaction import InteractionContext
 from app.chain.site import SiteChain, site_interaction_manager
-from app.chain.skills import skills_interaction_manager
+from app.application.messaging.skill import skill_interaction_manager
 from app.chain.subscribe import SubscribeChain, subscribe_interaction_manager
 from app.schemas.types import MessageChannel
 
 
 class TestSlashCommandInteractions(unittest.TestCase):
     def tearDown(self):
-        skills_interaction_manager.clear()
+        skill_interaction_manager.clear()
         site_interaction_manager.clear()
         subscribe_interaction_manager.clear()
 
     def test_message_routes_text_reply_to_latest_sites_interaction(self):
         chain = MessageChain()
-        skills_interaction_manager.create_or_replace(
+        skill_interaction_manager.create_or_replace(
             user_id="10001",
             channel=MessageChannel.Wechat,
             source="wechat-test",
@@ -43,7 +44,7 @@ class TestSlashCommandInteractions(unittest.TestCase):
             "app.chain.message.SiteChain.handle_text_interaction",
             return_value=True,
         ) as handle_site, patch(
-            "app.chain.message.SkillsChain.handle_text_interaction"
+            "app.chain.message.SkillInteractionHandler.handle_text_interaction"
         ) as handle_skills:
             chain.handle_message(
                 channel=MessageChannel.Wechat,
@@ -105,11 +106,13 @@ class TestSlashCommandInteractions(unittest.TestCase):
             return_value=True,
         ) as handle_callback:
             chain._handle_callback(
-                text=f"CALLBACK:sites:{request.request_id}:refresh",
-                channel=MessageChannel.Telegram,
-                source="telegram-test",
-                userid="10001",
-                username="tester",
+                callback_data=f"sites:{request.request_id}:refresh",
+                context=InteractionContext(
+                    channel=MessageChannel.Telegram,
+                    source="telegram-test",
+                    user_id="10001",
+                    username="tester",
+                ),
             )
 
         handle_callback.assert_called_once()
@@ -129,11 +132,13 @@ class TestSlashCommandInteractions(unittest.TestCase):
             return_value=True,
         ) as handle_callback:
             chain._handle_callback(
-                text=f"CALLBACK:subscribes:{request.request_id}:refresh",
-                channel=MessageChannel.Telegram,
-                source="telegram-test",
-                userid="10001",
-                username="tester",
+                callback_data=f"subscribes:{request.request_id}:refresh",
+                context=InteractionContext(
+                    channel=MessageChannel.Telegram,
+                    source="telegram-test",
+                    user_id="10001",
+                    username="tester",
+                ),
             )
 
         handle_callback.assert_called_once()