fix: 三端联调测试 2 P0 + 6 P1 + 2 P2 修复

P0-1: SaaS relay 模型别名解析 — "glm-4-flash" → "glm-4-flash-250414" (resolve_model)
P0-2: config.rs interpolate_env_vars UTF-8 修复 (chars 迭代器替代 bytes as char)
      + DB 启动编码检查 + docker-compose UTF-8 编码参数

P1-3: UI 模型选择器覆盖 Agent 默认模型 (model_override 全链路: TS→Tauri→Rust kernel)
P1-6: 知识搜索管道修复 — seed_knowledge 创建 chunks + 默认分类 (seed/uploaded/distillation)
P1-7: 用量限额从当前 Plan 读取 (非 stale usage 表)
P1-8: relay 双维度配额检查 (relay_requests + input_tokens)

P2-9: SSE 路径 token 计数修复 — 流结束检测替代固定 500ms sleep + billing increment

desktop/src-tauri/src/kernel_commands/chat.rs

@@ -30,6 +30,9 @@ pub struct ChatRequest {
     /// Enable sub-agent delegation (Ultra mode only)
     #[serde(default)]
     pub subagent_enabled: Option<bool>,
+    /// Model override — UI 选择的模型优先于 Agent 配置的默认模型
+    #[serde(default)]
+    pub model: Option<String>,
 }
 
 /// Chat response
@@ -76,6 +79,9 @@ pub struct StreamChatRequest {
     /// Enable sub-agent delegation (Ultra mode only)
     #[serde(default)]
     pub subagent_enabled: Option<bool>,
+    /// Model override — UI 选择的模型优先于 Agent 配置的默认模型
+    #[serde(default)]
+    pub model: Option<String>,
 }
 
 // ---------------------------------------------------------------------------
@@ -116,7 +122,7 @@ pub async fn agent_chat(
         None
     };
 
-    let response = kernel.send_message_with_chat_mode(&id, request.message, chat_mode)
+    let response = kernel.send_message_with_chat_mode(&id, request.message, chat_mode, request.model)
         .await
         .map_err(|e| format!("Chat failed: {}", e))?;
 
@@ -257,6 +263,7 @@ pub async fn agent_chat_stream(
             prompt_arg,
             session_id_parsed,
             Some(chat_mode_config),
+            request.model.clone(),
         )
             .await
             .map_err(|e| {