Remove unused 404 handler

The default appType == 'spa' in vite redirects all (unclaimed) paths to /index.html.

If needed, this can be disabled:
https://stackoverflow.com/questions/69701743/how-can-i-configure-vites-dev-server-to-give-404-errors/69711988#69711988

web/apps/payments/src/pages/404.tsx

@@ -1,9 +0,0 @@
-import { Container } from "components/Container";
-import React from "react";
-import S from "utils/strings";
-
-const Page: React.FC = () => {
-    return <Container>{S.error_404}</Container>;
-};
-
-export default Page;

web/apps/payments/src/utils/strings.ts

@@ -7,7 +7,6 @@
  */
 const S = {
     error_generic: "Oops, something went wrong.",
-    error_404: "404 | This page could not be found.",
 };
 
 export default S;

web/apps/payments/src/vite-env.d.ts

@@ -1,5 +1,9 @@
+/* Type shims provided by vite, e.g. for asset imports
+   https://vitejs.dev/guide/features.html#client-types */
+
 /// <reference types="vite/client" />
 
+/** Types for the vite injected environment variables */
 interface ImportMetaEnv {
     /**
      * Override the origin (scheme://host:port) of Ente's API to connect to.

web/packages/build-config/tsconfig-vite.json

@@ -4,6 +4,9 @@
      * The base configuration was generated using `yarn create vite`. This was
      * already almost the same as the `tsconfig-typecheck.json` we use
      * elsewhere, with one or two differences.
+     *
+     * For more details about the flags vite cares about, see
+     * https://vitejs.dev/guide/features.html#typescript-compiler-options
      */
     "compilerOptions": {
         "target": "ES2020",