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/lib/kernel-chat.ts

@@ -60,6 +60,7 @@ export function installChatMethods(ClientClass: { prototype: KernelClient }): vo
       reasoning_effort?: string;
       plan_mode?: boolean;
       subagent_enabled?: boolean;
+      model?: string;
     }
   ): Promise<{ runId: string }> {
     const runId = crypto.randomUUID();
@@ -199,6 +200,7 @@ export function installChatMethods(ClientClass: { prototype: KernelClient }): vo
           reasoningEffort: opts?.reasoning_effort,
           planMode: opts?.plan_mode,
           subagentEnabled: opts?.subagent_enabled,
+          model: opts?.model,
         },
       });
     } catch (err: unknown) {