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/store/chat/streamStore.ts

@@ -303,6 +303,9 @@ export const useStreamStore = create<StreamState>()(
         .map(m => ({ role: m.role, content: m.content }))
         .slice(-20);
 
+      // UI 模型选择器应覆盖 Agent 默认模型
+      const currentModel = useConversationStore.getState().currentModel;
+
       const result = await client.chatStream(
         content,
         {
@@ -534,6 +537,7 @@ export const useStreamStore = create<StreamState>()(
             set({ isStreaming: false, activeRunId: null });
           },
         },
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
         {
           sessionKey: effectiveSessionKey,
           agentId: effectiveAgentId,
@@ -542,7 +546,8 @@ export const useStreamStore = create<StreamState>()(
           plan_mode: get().getChatModeConfig().plan_mode,
           subagent_enabled: get().getChatModeConfig().subagent_enabled,
           history,
-        }
+          model: currentModel || undefined,
+        } as Parameters<typeof client.chatStream>[2]
       );
 
       if (result?.runId) {