fix(intelligence): 精确化 dead_code 标注并实现 LLM 上下文压缩

- 将 intelligence/llm/memory/browser 模块的 dead_code 注释从模糊的
  "reserved for future" 改为明确说明 Tauri invoke_handler 运行时注册机制
- 为 identity.rs 中 3 个真正未使用的方法添加 #[allow(dead_code)]
- 实现 compactor use_llm: true 功能：新增 compact_with_llm 方法和
  compactor_compact_llm Tauri 命令，支持 LLM 驱动的对话摘要生成
- 将 pipeline_commands.rs 中 40+ 处 println!/eprintln! 调试输出替换为
  tracing::debug!/warn!/error! 结构化日志
- 移除 intelligence/mod.rs 中不必要的 #[allow(unused_imports)]

desktop/src-tauri/src/intelligence/identity.rs

@@ -12,7 +12,11 @@
 //!
 //! NOTE: Some methods are reserved for future integration.
 
-#![allow(dead_code)] // Methods reserved for future identity management features
+// NOTE: #[tauri::command] functions are registered via invoke_handler! at runtime,
+// which the Rust compiler does not track as "use". This module-level allow is
+// required for all Tauri-commanded functions. Only genuinely unused non-command
+// methods have individual #[allow(dead_code)] annotations below.
+#![allow(dead_code)]
 
 use chrono::Utc;
 use serde::{Deserialize, Serialize};
@@ -493,11 +497,13 @@ impl AgentIdentityManager {
     }
 
     /// Export all identities for backup
+    #[allow(dead_code)] // Reserved: no Tauri command yet
     pub fn export_all(&self) -> HashMap<String, IdentityFiles> {
         self.identities.clone()
     }
 
     /// Import identities from backup
+    #[allow(dead_code)] // Reserved: no Tauri command yet
     pub fn import(&mut self, identities: HashMap<String, IdentityFiles>) {
         for (agent_id, files) in identities {
             self.identities.insert(agent_id, files);
@@ -506,6 +512,7 @@ impl AgentIdentityManager {
     }
 
     /// Get all proposals (for debugging)
+    #[allow(dead_code)] // Reserved: no Tauri command yet
     pub fn get_all_proposals(&self) -> &[IdentityChangeProposal] {
         &self.proposals
     }