Extract Vue frontend into separate container and add stp_wasm crate

Move Vue app from nginx/vue/ to top-level vue/ with its own Dockerfile,
update docker-compose configs and nginx proxy to serve from the new
container, and add initial Rust WASM crate (stp_wasm). Also fix .gitignore
to exclude Rust target/ directories.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vue/src/App.vue

@@ -0,0 +1,12 @@
+<script setup>
+import { RouterView } from "vue-router";
+import Navbar from "@/components/Navbar.vue";
+import Footer from "@/components/Footer.vue";
+</script>
+
+<template>
+    <Navbar class="no-print sticky" />
+    <RouterView />
+
+    <!-- <Footer style="height: 10vh" /> -->
+</template>