proper user/session creation and auth integration into UI

src/app/page.tsx

@@ -143,6 +143,13 @@ export default function HomePage() {
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({ prompt: aiPrompt })
       })
+      
+      if (res.status === 401) {
+        alert('Please sign in to use AI features.')
+        setAiLoading(false)
+        return
+      }
+      
       const data = await res.json()
 
       if (Array.isArray(data) && data.length > 0) {
@@ -225,25 +232,32 @@ export default function HomePage() {
         <div className='max-w-fit m-auto'> Drag & Drop *.ics here</div>
       </div>
       {/* AI Toolbar */}
-      <div className="flex flex-row gap-4 mb-4 items-start">
-        {session?.user && (
-          <>
-            <div className='w-full'>
-              <Textarea
-                className="wrap-anywhere min-h-12"
-                placeholder='Describe event for AI to create'
-                value={aiPrompt}
-                onChange={e => setAiPrompt(e.target.value)}
-              />
-            </div>
-            <div className='flex flex-row gap-2 pt-1.5'>
-              <Button onClick={handleAiCreate} disabled={aiLoading}>
-                {aiLoading ? 'Thinking...' : 'AI Create'}
-              </Button>
-            </div>
-          </>
-        )}
-      </div>
+      {session?.user ? (
+        <div className="flex flex-row gap-4 mb-4 items-start">
+          <div className='w-full'>
+            <Textarea
+              className="wrap-anywhere min-h-12"
+              placeholder='Describe event for AI to create'
+              value={aiPrompt}
+              onChange={e => setAiPrompt(e.target.value)}
+            />
+          </div>
+          <div className='flex flex-row gap-2 pt-1.5'>
+            <Button onClick={handleAiCreate} disabled={aiLoading}>
+              {aiLoading ? 'Thinking...' : 'AI Create'}
+            </Button>
+          </div>
+        </div>
+      ) : (
+        <div className="mb-4 p-4 border border-dashed rounded-lg text-center">
+          <div className="text-sm text-muted-foreground mb-2">
+            Sign in to unlock AI-powered calendar features
+          </div>
+          <Button variant="outline" size="sm" asChild>
+            <a href="/signin">Sign In</a>
+          </Button>
+        </div>
+      )}
 
       {/* Summary Panel */}
       {