Refactor IPC and DTO structures; remove unused code and streamline message handling

- Removed unused structs and methods from `response.rs`, `usage.rs`, and `client.rs`.
- Simplified `Connection` handling in `conn.rs` to only support Unix sockets.
- Updated `IpcServer` to exclusively use Unix sockets and removed TCP handling.
- Cleaned up `editlog.rs` by removing loading and recent entry methods.
- Refactored `memory.rs` to eliminate unused functions related to lesson promotion and retrospective creation.
- Enhanced `search.rs` to support multiple search providers and improved error handling.
- Updated chat view logic to simplify message display and improve user experience.
- Removed deprecated modules and constants from various files to streamline the codebase.

src/service/oauth/loopback.rs

@@ -13,10 +13,6 @@ impl LoopbackServer {
         Ok(LoopbackServer { listener, port })
     }
 
-    pub fn port(&self) -> u16 {
-        self.port
-    }
-
     pub fn redirect_uri(&self) -> String {
         format!("http://127.0.0.1:{}/callback", self.port)
     }

src/service/oauth/manager.rs

@@ -10,15 +10,6 @@ pub struct OAuthToken {
 }
 
 impl OAuthToken {
-    pub fn is_expired(&self) -> bool {
-        let now = SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs();
-        now >= self.expires_at
-    }
-
-    pub fn remaining_secs(&self) -> i64 {
-        let now = SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs();
-        self.expires_at as i64 - now as i64
-    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -92,52 +83,6 @@ impl OAuthManager {
         Ok(())
     }
 
-    pub fn refresh_token(&mut self) -> Result<(), String> {
-        let refresh_token = self.token.as_ref()
-            .and_then(|t| t.refresh_token.clone())
-            .ok_or("no refresh token available")?;
-
-        let mut params = std::collections::HashMap::new();
-        params.insert("grant_type", "refresh_token");
-        params.insert("refresh_token", &refresh_token);
-        params.insert("client_id", &self.config.client_id);
-
-        let resp = self.client
-            .post(&self.config.token_url)
-            .form(&params)
-            .send()
-            .map_err(|e| format!("refresh failed: {}", e))?;
-
-        let status = resp.status();
-        let body: serde_json::Value = resp.json().map_err(|e| format!("parse failed: {}", e))?;
-
-        if !status.is_success() {
-            return Err(format!("refresh endpoint returned {}: {}", status, body));
-        }
-
-        let access_token = body["access_token"].as_str().ok_or("missing access_token")?.to_string();
-        let expires_in = body["expires_in"].as_u64().unwrap_or(3600);
-        let now = SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_secs();
-
-        self.token = Some(OAuthToken {
-            access_token,
-            refresh_token: body["refresh_token"].as_str().map(|s| s.to_string()).or(self.token.as_ref().and_then(|t| t.refresh_token.clone())),
-            expires_at: now + expires_in,
-            token_type: body["token_type"].as_str().unwrap_or("Bearer").to_string(),
-        });
-
-        Ok(())
-    }
-
-    pub fn ensure_token(&mut self) -> Result<(), String> {
-        if let Some(ref token) = self.token {
-            if token.remaining_secs() < 60 {
-                return self.refresh_token();
-            }
-        }
-        Ok(())
-    }
-
     pub fn build_auth_url(&self, redirect_uri: &str, state: &str, code_challenge: &str) -> String {
         let mut url = url::Url::parse(&self.config.auth_url).unwrap_or_else(|_| url::Url::parse("https://example.com").unwrap());
         url.query_pairs_mut()