feat(appearance): add theme color picker, zoom level selector, reset button

外观设置页新增三个 UI 单元：12 个 shadcn 主题预设的色盘按钮网格、6 档窗口缩放
下拉选择器、以及只重置主题色和缩放（不动主题模式）的恢复默认按钮。
i18n 键在上一个 Task 中已预备好，本提交后整个外观设置功能即可在浏览器中端到端使用。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/settings/appearance-settings.tsx

@@ -1,8 +1,9 @@
 "use client"
 
-import { Monitor, Moon, Sun } from "lucide-react"
+import { Monitor, Moon, RotateCcw, Sun, Type } from "lucide-react"
 import { useTranslations } from "next-intl"
 import { useTheme } from "next-themes"
+import { Button } from "@/components/ui/button"
 import {
   Select,
   SelectContent,
@@ -10,12 +11,26 @@ import {
   SelectTrigger,
   SelectValue,
 } from "@/components/ui/select"
+import { useThemeColor, useZoomLevel } from "@/hooks/use-appearance"
+import { cn } from "@/lib/utils"
+import {
+  DEFAULT_THEME_COLOR,
+  DEFAULT_ZOOM_LEVEL,
+  THEME_COLOR_PREVIEW,
+  THEME_COLORS,
+  ZOOM_LEVELS,
+  type ThemeColor,
+  type ZoomLevel,
+} from "@/lib/theme-presets"
 
 type ThemeMode = "system" | "light" | "dark"
 
 export function AppearanceSettings() {
   const t = useTranslations("AppearanceSettings")
   const { theme, resolvedTheme, setTheme } = useTheme()
+  const { themeColor, setThemeColor } = useThemeColor()
+  const { zoomLevel, setZoomLevel } = useZoomLevel()
+
   const resolvedThemeLabel =
     resolvedTheme === "dark"
       ? t("resolvedTheme.dark")
@@ -23,9 +38,18 @@ export function AppearanceSettings() {
         ? t("resolvedTheme.light")
         : t("resolvedTheme.unknown")
 
+  const isAtDefaults =
+    themeColor === DEFAULT_THEME_COLOR && zoomLevel === DEFAULT_ZOOM_LEVEL
+
+  const handleResetToDefaults = () => {
+    setThemeColor(DEFAULT_THEME_COLOR)
+    setZoomLevel(DEFAULT_ZOOM_LEVEL)
+  }
+
   return (
     <div className="h-full overflow-auto">
       <div className="w-full space-y-4">
+        {/* ===== Theme Mode (existing) ===== */}
         <section className="rounded-xl border bg-card p-4 space-y-4">
           <div className="flex items-center gap-2">
             <Sun className="h-4 w-4 text-muted-foreground" />
@@ -76,6 +100,112 @@ export function AppearanceSettings() {
             </p>
           </div>
         </section>
+
+        {/* ===== Theme Color (new) ===== */}
+        <section className="rounded-xl border bg-card p-4 space-y-4">
+          <div className="flex items-center gap-2">
+            <span
+              className="size-4 rounded-full border"
+              style={{ backgroundColor: THEME_COLOR_PREVIEW[themeColor] }}
+              aria-hidden
+            />
+            <h2 className="text-sm font-semibold">
+              {t("themeColor.sectionTitle")}
+            </h2>
+          </div>
+
+          <p className="text-xs text-muted-foreground leading-5">
+            {t("themeColor.sectionDescription")}
+          </p>
+
+          <div className="grid grid-cols-3 gap-2 sm:grid-cols-4 md:grid-cols-6">
+            {THEME_COLORS.map((color) => {
+              const isActive = themeColor === color
+              return (
+                <button
+                  key={color}
+                  type="button"
+                  onClick={() => setThemeColor(color as ThemeColor)}
+                  aria-pressed={isActive}
+                  className={cn(
+                    "flex items-center gap-2 rounded-md border px-3 py-2 text-xs transition-colors",
+                    "hover:bg-accent hover:text-accent-foreground",
+                    isActive && "border-primary ring-2 ring-primary/30"
+                  )}
+                >
+                  <span
+                    className="size-4 shrink-0 rounded-full border"
+                    style={{ backgroundColor: THEME_COLOR_PREVIEW[color] }}
+                    aria-hidden
+                  />
+                  <span className="truncate">
+                    {t(`themeColor.options.${color}`)}
+                  </span>
+                </button>
+              )
+            })}
+          </div>
+
+          <p className="text-[11px] text-muted-foreground">
+            {t("themeColor.current", {
+              color: t(`themeColor.options.${themeColor}`),
+            })}
+          </p>
+        </section>
+
+        {/* ===== Zoom Level (new) ===== */}
+        <section className="rounded-xl border bg-card p-4 space-y-4">
+          <div className="flex items-center gap-2">
+            <Type className="h-4 w-4 text-muted-foreground" />
+            <h2 className="text-sm font-semibold">
+              {t("zoomLevel.sectionTitle")}
+            </h2>
+          </div>
+
+          <p className="text-xs text-muted-foreground leading-5">
+            {t("zoomLevel.sectionDescription")}
+          </p>
+
+          <div className="space-y-2">
+            <Select
+              value={String(zoomLevel)}
+              onValueChange={(value) =>
+                setZoomLevel(parseInt(value, 10) as ZoomLevel)
+              }
+            >
+              <SelectTrigger className="w-56">
+                <SelectValue placeholder={t("zoomLevel.placeholder")} />
+              </SelectTrigger>
+              <SelectContent align="start">
+                {ZOOM_LEVELS.map((z) => (
+                  <SelectItem key={z} value={String(z)}>
+                    {z}%
+                    {z === DEFAULT_ZOOM_LEVEL
+                      ? ` (${t("zoomLevel.default")})`
+                      : ""}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+            <p className="text-[11px] text-muted-foreground">
+              {t("zoomLevel.current", { zoom: zoomLevel })}
+            </p>
+          </div>
+        </section>
+
+        {/* ===== Reset to defaults (new) ===== */}
+        <div className="flex justify-end">
+          <Button
+            variant="outline"
+            size="sm"
+            disabled={isAtDefaults}
+            onClick={handleResetToDefaults}
+            title={t("resetHint")}
+          >
+            <RotateCcw className="mr-2 h-3.5 w-3.5" />
+            {t("resetToDefaults")}
+          </Button>
+        </div>
       </div>
     </div>
   )