AppForge: migrate off Supabase to external Postgres + Better Auth + local storage

- New Express + TypeScript backend (server/) with pg, Better Auth, local file storage
- De-Supabased Postgres schema (server/db) and TS reimplementations of DB functions
- Frontend data layer rewired to REST (rest-client + backend-client compat shim)
- Removed all Supabase references (code, config, deps, docs)
- New brand assets: gradient favicon/app icons + dark/white wordmark logos

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/BackToTop.tsx

@@ -0,0 +1,49 @@
+import { useState, useEffect } from "react";
+import { ArrowUp } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import { motion, AnimatePresence } from "framer-motion";
+
+const BackToTop = () => {
+  const [isVisible, setIsVisible] = useState(false);
+
+  useEffect(() => {
+    const toggleVisibility = () => {
+      setIsVisible(window.scrollY > 400);
+    };
+
+    window.addEventListener("scroll", toggleVisibility);
+    return () => window.removeEventListener("scroll", toggleVisibility);
+  }, []);
+
+  const scrollToTop = () => {
+    window.scrollTo({
+      top: 0,
+      behavior: "smooth",
+    });
+  };
+
+  return (
+    <AnimatePresence>
+      {isVisible && (
+        <motion.div
+          initial={{ opacity: 0, scale: 0.8 }}
+          animate={{ opacity: 1, scale: 1 }}
+          exit={{ opacity: 0, scale: 0.8 }}
+          transition={{ duration: 0.2 }}
+          className="fixed bottom-6 right-6 z-50"
+        >
+          <Button
+            onClick={scrollToTop}
+            size="icon"
+            className="h-12 w-12 rounded-full shadow-lg bg-primary hover:bg-primary/90 text-primary-foreground"
+            aria-label="Back to top"
+          >
+            <ArrowUp className="h-5 w-5" />
+          </Button>
+        </motion.div>
+      )}
+    </AnimatePresence>
+  );
+};
+
+export default BackToTop;