docs: 统一 README，删除冗余文档；refactor: 消除全部 15 个 warning

- 新建 README.md，整合项目架构、命令、配置、数据流
- 删除 6 个冗余/过时 md 文档
- save_summary_to_db 委托 db::models::save_summary，避免 SQL 重复
- #[allow(dead_code)] 标注 serde 反序列化字段和预留 API
- 移除未使用的 re-export (Summarizer, Message, Role, StreamChunk)
- 修复 README 中 manage_memos 风险等级和缺失的 AMAP_KEY 配置

src/wechat/types.rs

@@ -145,9 +145,13 @@ pub struct MessageItem {
 
 impl MessageItem {
     pub const TYPE_TEXT: i32 = 1;
+    #[allow(dead_code)]
     pub const TYPE_IMAGE: i32 = 2;
+    #[allow(dead_code)]
     pub const TYPE_VOICE: i32 = 3;
+    #[allow(dead_code)]
     pub const TYPE_FILE: i32 = 4;
+    #[allow(dead_code)]
     pub const TYPE_VIDEO: i32 = 5;
 
     pub fn text(text: &str) -> Self {
@@ -235,6 +239,7 @@ impl Default for WeixinMessage {
 }
 
 impl WeixinMessage {
+    #[allow(dead_code)]
     pub const TYPE_NONE: i32 = 0;
     pub const TYPE_USER: i32 = 1;
     pub const TYPE_BOT: i32 = 2;
@@ -296,6 +301,7 @@ pub struct GetUpdatesResp {
     #[serde(default)]
     pub get_updates_buf: String,
     #[serde(skip_serializing_if = "Option::is_none")]
+    #[allow(dead_code)]
     pub longpolling_timeout_ms: Option<i64>,
 }
 
@@ -320,11 +326,13 @@ pub struct LoginResult {
     pub token: String,
     pub account_id: String,
     pub base_url: String,
+    #[allow(dead_code)]
     pub user_id: String,
 }
 
 /// 收到的消息事件
 #[derive(Debug, Clone)]
+#[allow(dead_code)]
 pub struct MessageEvent {
     pub from_user_id: String,
     pub text: String,