fix(security): sanitize error logging and remove Zod schema details from responses

- Stripe webhook: log only error.message instead of full error objects
  to avoid exposing stack traces in aggregated logs
- Admin products POST: return only first Zod error message instead of
  the full error array which reveals internal schema structure

app/src/app/api/admin/products/route.ts

@@ -16,8 +16,8 @@ export async function GET(request: NextRequest) {
   if (!user) return NextResponse.json({ error: 'Forbidden' }, { status: 403 })
 
   const { searchParams } = new URL(request.url)
-  const page = parseInt(searchParams.get('page') || '1')
+  const page = Math.max(1, parseInt(searchParams.get('page') || '1') || 1)
-  const limit = parseInt(searchParams.get('limit') || '20')
+  const limit = Math.min(100, Math.max(1, parseInt(searchParams.get('limit') || '20') || 20))
   const search = searchParams.get('search')
   const status = searchParams.get('status')
 
@@ -65,7 +65,7 @@ export async function POST(request: NextRequest) {
   const parsed = productSchema.safeParse(body)
   if (!parsed.success) {
     return NextResponse.json(
-      { error: parsed.error.errors[0]?.message || 'Invalid input', details: parsed.error.errors },
+      { error: parsed.error.errors[0]?.message ?? 'Invalid input' },
       { status: 400 }
     )
   }

app/src/app/api/webhooks/stripe/route.ts

@@ -16,7 +16,7 @@ export async function POST(request: NextRequest) {
   try {
     event = constructWebhookEvent(body, signature, process.env.STRIPE_WEBHOOK_SECRET!)
   } catch (err) {
-    console.error('Webhook signature verification failed:', err)
+    console.error('Webhook signature verification failed:', err instanceof Error ? err.message : String(err))
     return NextResponse.json({ error: 'Invalid signature' }, { status: 400 })
   }
 
@@ -55,7 +55,7 @@ export async function POST(request: NextRequest) {
               currency: order.currency,
             })
           } catch (emailErr) {
-            console.error('Failed to send confirmation email:', emailErr)
+            console.error('Failed to send confirmation email:', emailErr instanceof Error ? emailErr.message : String(emailErr))
           }
         }
 
@@ -116,7 +116,7 @@ export async function POST(request: NextRequest) {
         console.log(`Unhandled event type: ${event.type}`)
     }
   } catch (err) {
-    console.error('Error processing webhook:', err)
+    console.error('Error processing webhook:', err instanceof Error ? err.message : String(err))
     return NextResponse.json({ error: 'Webhook processing failed' }, { status: 500 })
   }