feat(ai): Day 7 — 会话持久化 Entity + Service

- 新增 3 个 SeaORM Entity: ai_chat_session / ai_chat_message / ai_tool_call_log
- ChatSessionService: create / list / get / close / rename
- ChatMessageService: save_message / list_messages / save_tool_call_log
- 参数封装为 SaveMessageParams / SaveToolCallLogParams 避免 clippy too_many_arguments
- AiState 注册 chat_session + chat_message 服务
- erp-server main.rs 初始化注入

crates/erp-ai/src/state.rs

@@ -7,6 +7,8 @@ use sea_orm::DatabaseConnection;
 use crate::provider::registry::ProviderRegistry;
 use crate::service::analysis::AnalysisService;
 use crate::service::cache::CacheService;
+use crate::service::chat_message::ChatMessageService;
+use crate::service::chat_session::ChatSessionService;
 use crate::service::feature_flag_service::FeatureFlagService;
 use crate::service::insight_service::InsightService;
 use crate::service::knowledge::KnowledgeService;
@@ -32,4 +34,6 @@ pub struct AiState {
     pub insight_service: Arc<InsightService>,
     pub feature_flags: Arc<FeatureFlagService>,
     pub knowledge: Arc<KnowledgeService>,
+    pub chat_session: Arc<ChatSessionService>,
+    pub chat_message: Arc<ChatMessageService>,
 }