feat: AI provider testing page + multi-provider support + UX design spec

- Add AI Provider Testing page (/admin/ai-test) with Tags and Embeddings tests
- Add new AI providers: CustomOpenAI, DeepSeek, OpenRouter
- Add API routes for AI config, models listing, and testing endpoints
- Add UX Design Specification document for Phase 1 MVP AI
- Add PRD Phase 1 MVP AI planning document
- Update admin settings and sidebar navigation
- Fix AI factory for multi-provider support

keep-notes/app/(main)/admin/ai-test/page.tsx

@@ -0,0 +1,106 @@
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
+import { Button } from '@/components/ui/button'
+import { auth } from '@/auth'
+import { redirect } from 'next/navigation'
+import Link from 'next/link'
+import { ArrowLeft, TestTube } from 'lucide-react'
+import { AI_TESTER } from './ai-tester'
+
+export default async function AITestPage() {
+  const session = await auth()
+
+  if ((session?.user as any)?.role !== 'ADMIN') {
+    redirect('/')
+  }
+
+  return (
+    <div className="container mx-auto py-10 px-4 max-w-6xl">
+      <div className="flex justify-between items-center mb-8">
+        <div className="flex items-center gap-3">
+          <Link href="/admin/settings">
+            <Button variant="outline" size="icon">
+              <ArrowLeft className="h-4 w-4" />
+            </Button>
+          </Link>
+          <div>
+            <h1 className="text-3xl font-bold flex items-center gap-2">
+              <TestTube className="h-8 w-8" />
+              AI Provider Testing
+            </h1>
+            <p className="text-muted-foreground mt-1">
+              Test your AI providers for tag generation and semantic search embeddings
+            </p>
+          </div>
+        </div>
+      </div>
+
+      <div className="grid gap-6 md:grid-cols-2">
+        {/* Tags Provider Test */}
+        <Card className="border-blue-200 dark:border-blue-900">
+          <CardHeader className="bg-blue-50/50 dark:bg-blue-950/20">
+            <CardTitle className="flex items-center gap-2">
+              <span className="text-2xl">🏷️</span>
+              Tags Generation Test
+            </CardTitle>
+            <CardDescription>
+              Test the AI provider responsible for automatic tag suggestions
+            </CardDescription>
+          </CardHeader>
+          <CardContent className="pt-6">
+            <AI_TESTER type="tags" />
+          </CardContent>
+        </Card>
+
+        {/* Embeddings Provider Test */}
+        <Card className="border-green-200 dark:border-green-900">
+          <CardHeader className="bg-green-50/50 dark:bg-green-950/20">
+            <CardTitle className="flex items-center gap-2">
+              <span className="text-2xl">🔍</span>
+              Embeddings Test
+            </CardTitle>
+            <CardDescription>
+              Test the AI provider responsible for semantic search embeddings
+            </CardDescription>
+          </CardHeader>
+          <CardContent className="pt-6">
+            <AI_TESTER type="embeddings" />
+          </CardContent>
+        </Card>
+      </div>
+
+      {/* Info Section */}
+      <Card className="mt-6">
+        <CardHeader>
+          <CardTitle>ℹ️ How Testing Works</CardTitle>
+        </CardHeader>
+        <CardContent className="space-y-4 text-sm">
+          <div>
+            <h4 className="font-semibold mb-2">🏷️ Tags Generation Test:</h4>
+            <ul className="list-disc list-inside space-y-1 text-muted-foreground">
+              <li>Sends a sample note to the AI provider</li>
+              <li>Requests 3-5 relevant tags based on the content</li>
+              <li>Displays the generated tags with confidence scores</li>
+              <li>Measures response time</li>
+            </ul>
+          </div>
+          <div>
+            <h4 className="font-semibold mb-2">🔍 Embeddings Test:</h4>
+            <ul className="list-disc list-inside space-y-1 text-muted-foreground">
+              <li>Sends a sample text to the embedding provider</li>
+              <li>Generates a vector representation (list of numbers)</li>
+              <li>Displays embedding dimensions and sample values</li>
+              <li>Verifies the vector is valid and properly formatted</li>
+            </ul>
+          </div>
+          <div className="bg-amber-50 dark:bg-amber-950/20 p-4 rounded-lg border border-amber-200 dark:border-amber-900">
+            <p className="font-semibold text-amber-900 dark:text-amber-100">💡 Tip:</p>
+            <p className="text-amber-800 dark:text-amber-200 mt-1">
+              You can use different providers for tags and embeddings! For example, use Ollama (free) for tags
+              and OpenAI (best quality) for embeddings to optimize costs and performance.
+            </p>
+          </div>
+        </CardContent>
+      </Card>
+    </div>
+  )
+}