fix(i18n): fix language switcher bug and refine Chinese translations

Motivation:
The language switcher's change event listener was never registered because () does not support an initialization callback as its 4th argument. Additionally, the Chinese translation for 'LLM Manager' was inaccurate (模型管家).

Implementation:
1. Replaced the unsupported  callback with an IIFE to manually create the select element, set its value, and add the 'change' event listener.
2. Updated 'I18N_DICT' to change '模型管家' to 'LLM 管理器' for better accuracy.

web/js/provider_manager.js

@@ -82,7 +82,7 @@ const I18N_DICT = {
         menu_tooltip: "Manage LLM API Providers & Model Config"
     },
     zh: {
-        manager_title: "LLMs 模型管家",
+        manager_title: "LLM 管理器",
         unsaved_title: "未保存更改",
         unsaved_msg: "你有未保存的更改。\\n确定要放弃它们吗？",
         cancel: "取消",
@@ -142,7 +142,7 @@ const I18N_DICT = {
         delete: "删除",
         preview: "预览: ",
         lang_switch: "EN",
-        menu_button: "LLM 模型管家",
+        menu_button: "LLM 管理器",
         menu_tooltip: "管理 LLM API 供应商与模型配置"
     }
 };
@@ -479,24 +479,25 @@ class ProviderManager {
                             style: { position: "absolute", left: "8px", display: "flex", pointerEvents: "none", color: "var(--glass-text-secondary)" },
                             innerHTML: `<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="icon icon-tabler icons-tabler-outline icon-tabler-language"><path stroke="none" d="M0 0h24v24H0z" fill="none"/><path d="M9 6.371c0 4.418 -2.239 6.629 -5 6.629" /><path d="M4 6.371h7" /><path d="M5 9c0 2.144 2.252 3.908 6 4" /><path d="M12 20l4 -9l4 9" /><path d="M19.1 18h-6.2" /><path d="M6.694 3 l.793 .582" /></svg>`
                         }),
-                        $el("select", {
-                            style: {
-                                background: "transparent",
-                                color: "var(--glass-text-primary)",
-                                border: "none",
-                                outline: "none",
-                                cursor: "pointer",
-                                padding: "6px 28px 6px 30px",
-                                appearance: "none",
-                                fontSize: "0.85em",
-                                fontFamily: "inherit"
-                            }
-                        }, [
-                            $el("option", { value: "zh", textContent: "简体中文" }),
-                            $el("option", { value: "en", textContent: "English" })
-                        ], (el) => {
-                            el.value = getLang();
-                            el.addEventListener("change", (e) => {
+                        (() => {
+                            const langSelect = $el("select", {
+                                style: {
+                                    background: "transparent",
+                                    color: "var(--glass-text-primary)",
+                                    border: "none",
+                                    outline: "none",
+                                    cursor: "pointer",
+                                    padding: "6px 28px 6px 30px",
+                                    appearance: "none",
+                                    fontSize: "0.85em",
+                                    fontFamily: "inherit"
+                                }
+                            }, [
+                                $el("option", { value: "zh", textContent: "简体中文" }),
+                                $el("option", { value: "en", textContent: "English" })
+                            ]);
+                            langSelect.value = getLang();
+                            langSelect.addEventListener("change", (e) => {
                                 localStorage.setItem("llm_pm_lang", e.target.value);
                                 // Re-render UI
                                 this.modal.remove();
@@ -511,7 +512,8 @@ class ProviderManager {
                                     menuBtn.title = t("menu_tooltip");
                                 }
                             });
-                        }),
+                            return langSelect;
+                        })(),
                         $el("div", {
                             style: { position: "absolute", right: "8px", display: "flex", pointerEvents: "none", color: "var(--glass-text-secondary)" },
                             innerHTML: `<svg xmlns="http://www.w3.org/2000/svg" width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><polyline points="6 9 12 15 18 9"></polyline></svg>`