feat: add working theme selector and improve settings UI

Added fully functional theme selector and improved the settings UI with
better components and cleaner copy.

Changes:
- Created Switch component (shadcn/radix-ui) for boolean settings
- Added working theme selector that integrates with existing theme system
- Uses useTheme hook to display available themes (Dark, Light, Plan9)
- Reordered sections: Appearance first, Post second
- Reordered settings: Theme first in Appearance section
- Replaced Checkbox with Switch for better UX on boolean toggles
- Simplified copy: "Add Grimoire tag to published events" instead of listing kinds
- Simplified copy: "Display client identifiers in events" instead of "via Grimoire" mention
- Better layout: Label/description on left, Switch on right

Settings now use proper form components:
- Switch for boolean toggles (include client tag, show client tags)
- Button group for theme selection
- Clean justify-between layout for settings rows

The theme selector works immediately - clicking Dark/Light/Plan9 applies
the theme instantly via the existing ThemeProvider context.

src/components/SettingsViewer.tsx

@@ -1,21 +1,73 @@
 import { Tabs, TabsContent, TabsList, TabsTrigger } from "./ui/tabs";
-import { Checkbox } from "./ui/checkbox";
+import { Switch } from "./ui/switch";
+import { Button } from "./ui/button";
 import { useSettings } from "@/hooks/useSettings";
+import { useTheme } from "@/lib/themes";
 
 export function SettingsViewer() {
   const { settings, updateSetting } = useSettings();
+  const { themeId, setTheme, availableThemes } = useTheme();
 
   return (
     <div className="h-full flex flex-col">
-      <Tabs defaultValue="post" className="flex-1 flex flex-col">
+      <Tabs defaultValue="appearance" className="flex-1 flex flex-col">
         <div className="border-b px-6 py-3">
           <TabsList>
-            <TabsTrigger value="post">Post</TabsTrigger>
             <TabsTrigger value="appearance">Appearance</TabsTrigger>
+            <TabsTrigger value="post">Post</TabsTrigger>
           </TabsList>
         </div>
 
         <div className="flex-1 overflow-y-auto">
+          <TabsContent value="appearance" className="m-0 p-6 space-y-6">
+            <div>
+              <h3 className="text-lg font-semibold mb-1">Appearance</h3>
+              <p className="text-sm text-muted-foreground">
+                Customize display preferences
+              </p>
+            </div>
+
+            <div className="space-y-6">
+              <div className="space-y-3">
+                <label className="text-sm">Theme</label>
+                <div className="flex gap-2">
+                  {availableThemes.map((theme) => (
+                    <Button
+                      key={theme.id}
+                      variant={themeId === theme.id ? "default" : "outline"}
+                      size="sm"
+                      onClick={() => setTheme(theme.id)}
+                      className="capitalize"
+                    >
+                      {theme.name}
+                    </Button>
+                  ))}
+                </div>
+              </div>
+
+              <div className="flex items-center justify-between">
+                <div className="space-y-0.5">
+                  <label
+                    htmlFor="show-client-tags"
+                    className="text-sm font-medium cursor-pointer"
+                  >
+                    Show client tags
+                  </label>
+                  <p className="text-sm text-muted-foreground">
+                    Display client identifiers in events
+                  </p>
+                </div>
+                <Switch
+                  id="show-client-tags"
+                  checked={settings?.appearance?.showClientTags ?? true}
+                  onCheckedChange={(checked: boolean) =>
+                    updateSetting("appearance", "showClientTags", checked)
+                  }
+                />
+              </div>
+            </div>
+          </TabsContent>
+
           <TabsContent value="post" className="m-0 p-6 space-y-6">
             <div>
               <h3 className="text-lg font-semibold mb-1">Post Settings</h3>
@@ -25,57 +77,25 @@ export function SettingsViewer() {
             </div>
 
             <div className="space-y-4">
-              <div className="flex items-start space-x-3">
-                <Checkbox
+              <div className="flex items-center justify-between">
+                <div className="space-y-0.5">
+                  <label
+                    htmlFor="include-client-tag"
+                    className="text-sm font-medium cursor-pointer"
+                  >
+                    Include client tag
+                  </label>
+                  <p className="text-sm text-muted-foreground">
+                    Add Grimoire tag to published events
+                  </p>
+                </div>
+                <Switch
                   id="include-client-tag"
                   checked={settings?.post?.includeClientTag ?? true}
                   onCheckedChange={(checked: boolean) =>
                     updateSetting("post", "includeClientTag", checked)
                   }
                 />
-                <div className="space-y-1">
-                  <label
-                    htmlFor="include-client-tag"
-                    className="text-sm cursor-pointer"
-                  >
-                    Include client tag
-                  </label>
-                  <p className="text-sm text-muted-foreground">
-                    Add Grimoire tag to posts, spells, and deletions
-                  </p>
-                </div>
-              </div>
-            </div>
-          </TabsContent>
-
-          <TabsContent value="appearance" className="m-0 p-6 space-y-6">
-            <div>
-              <h3 className="text-lg font-semibold mb-1">Appearance</h3>
-              <p className="text-sm text-muted-foreground">
-                Customize display preferences
-              </p>
-            </div>
-
-            <div className="space-y-4">
-              <div className="flex items-start space-x-3">
-                <Checkbox
-                  id="show-client-tags"
-                  checked={settings?.appearance?.showClientTags ?? true}
-                  onCheckedChange={(checked: boolean) =>
-                    updateSetting("appearance", "showClientTags", checked)
-                  }
-                />
-                <div className="space-y-1">
-                  <label
-                    htmlFor="show-client-tags"
-                    className="text-sm cursor-pointer"
-                  >
-                    Show client tags
-                  </label>
-                  <p className="text-sm text-muted-foreground">
-                    Display "via Grimoire" and other client identifiers
-                  </p>
-                </div>
               </div>
             </div>
           </TabsContent>

src/components/ui/switch.tsx

@@ -0,0 +1,27 @@
+import * as React from "react";
+import * as SwitchPrimitives from "@radix-ui/react-switch";
+
+import { cn } from "@/lib/utils";
+
+const Switch = React.forwardRef<
+  React.ElementRef<typeof SwitchPrimitives.Root>,
+  React.ComponentPropsWithoutRef<typeof SwitchPrimitives.Root>
+>(({ className, ...props }, ref) => (
+  <SwitchPrimitives.Root
+    className={cn(
+      "peer inline-flex h-5 w-9 shrink-0 cursor-pointer items-center rounded-full border-2 border-transparent shadow-sm transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 focus-visible:ring-offset-background disabled:cursor-not-allowed disabled:opacity-50 data-[state=checked]:bg-primary data-[state=unchecked]:bg-input",
+      className,
+    )}
+    {...props}
+    ref={ref}
+  >
+    <SwitchPrimitives.Thumb
+      className={cn(
+        "pointer-events-none block h-4 w-4 rounded-full bg-background shadow-lg ring-0 transition-transform data-[state=checked]:translate-x-4 data-[state=unchecked]:translate-x-0",
+      )}
+    />
+  </SwitchPrimitives.Root>
+));
+Switch.displayName = SwitchPrimitives.Root.displayName;
+
+export { Switch };