feat: add Resend integration for email verification and update package dependencies

- Integrated Resend for sending email verification upon user sign-up.
- Updated package.json to include Resend as a dependency.
- Enhanced authentication flow with error handling for email sending.
- Removed outdated Canvas Implementation Guide documentation.

app/(app)/canvas/[canvasId]/page.tsx

@@ -1,9 +1,10 @@
-import { redirect } from "next/navigation";
+import { notFound, redirect } from "next/navigation";
 
 import Canvas from "@/components/canvas/canvas";
 import CanvasToolbar from "@/components/canvas/canvas-toolbar";
+import { api } from "@/convex/_generated/api";
 import type { Id } from "@/convex/_generated/dataModel";
-import { isAuthenticated } from "@/lib/auth-server";
+import { fetchAuthQuery, isAuthenticated } from "@/lib/auth-server";
 
 export default async function CanvasPage({
   params,
@@ -18,6 +19,17 @@ export default async function CanvasPage({
   const { canvasId } = await params;
   const typedCanvasId = canvasId as Id<"canvases">;
 
+  try {
+    const canvas = await fetchAuthQuery(api.canvases.get, {
+      canvasId: typedCanvasId,
+    });
+    if (!canvas) {
+      notFound();
+    }
+  } catch {
+    notFound();
+  }
+
   return (
     <div className="relative h-screen w-screen overflow-hidden">
       <CanvasToolbar canvasId={typedCanvasId} />