feat: migrate to Next.js for Mini App and enhance project structure

- Replaced the previous webapp with a new Mini App built using Next.js, improving performance and maintainability.
- Updated the `.gitignore` to exclude Next.js build artifacts and node modules.
- Revised documentation in `AGENTS.md`, `README.md`, and `architecture.md` to reflect the new Mini App structure and technology stack.
- Enhanced Dockerfile to support the new build process for the Next.js application.
- Updated CI workflow to build and test the Next.js application.
- Added new configuration options for the Mini App, including `MINI_APP_SHORT_NAME` for improved deep linking.
- Refactored frontend testing setup to accommodate the new structure and testing framework.
- Removed legacy webapp files and dependencies to streamline the project.

webapp-next/src/components/AppErrorBoundary.tsx

@@ -0,0 +1,76 @@
+/**
+ * Error boundary that catches render errors in the app tree and shows a fallback
+ * with a reload option. Uses pure i18n (getLang/translate) so it does not depend
+ * on React context that might be broken.
+ */
+
+"use client";
+
+import React from "react";
+import { getLang } from "@/i18n/messages";
+import { translate } from "@/i18n/messages";
+import { Button } from "@/components/ui/button";
+
+interface AppErrorBoundaryProps {
+  children: React.ReactNode;
+}
+
+interface AppErrorBoundaryState {
+  hasError: boolean;
+}
+
+/**
+ * Catches JavaScript errors in the child tree and renders a fallback UI
+ * instead of crashing. Provides a Reload button to recover.
+ */
+export class AppErrorBoundary extends React.Component<
+  AppErrorBoundaryProps,
+  AppErrorBoundaryState
+> {
+  constructor(props: AppErrorBoundaryProps) {
+    super(props);
+    this.state = { hasError: false };
+  }
+
+  static getDerivedStateFromError(): AppErrorBoundaryState {
+    return { hasError: true };
+  }
+
+  componentDidCatch(error: Error, errorInfo: React.ErrorInfo): void {
+    if (typeof console !== "undefined" && console.error) {
+      console.error("AppErrorBoundary caught an error:", error, errorInfo);
+    }
+  }
+
+  handleReload = (): void => {
+    if (typeof window !== "undefined") {
+      window.location.reload();
+    }
+  };
+
+  render(): React.ReactNode {
+    if (this.state.hasError) {
+      const lang = getLang();
+      const message = translate(lang, "error_boundary.message");
+      const reloadLabel = translate(lang, "error_boundary.reload");
+      return (
+        <div
+          className="flex min-h-[200px] flex-col items-center justify-center gap-4 rounded-xl bg-surface py-8 px-4 text-center"
+          role="alert"
+        >
+          <p className="m-0 text-sm font-medium text-foreground">{message}</p>
+          <Button
+            type="button"
+            variant="default"
+            size="sm"
+            onClick={this.handleReload}
+            className="bg-primary text-primary-foreground hover:opacity-90"
+          >
+            {reloadLabel}
+          </Button>
+        </div>
+      );
+    }
+    return this.props.children;
+  }
+}