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/views/admin/Login.vue

@@ -0,0 +1,34 @@
+<script setup>
+import { ref, onMounted, computed } from "vue";
+import { useAuthStore } from "@/stores/auth";
+
+import Button from "@/components/input/Button.vue";
+
+const auth = useAuthStore();
+const username = ref("");
+const password = ref("");
+
+function handleLogin() {
+    auth.logIn(username.value, password.value);
+}
+
+function handleLogout() {
+    auth.logOut();
+}
+</script>
+
+<template>
+    <div v-if="auth.loggedIn" class="flex flex-col">
+        <h1>Logged in</h1>
+        <p>{{ auth.user.id }}</p>
+        <p>{{ auth.user.username }}</p>
+        <p>{{ auth.user.admin }}</p>
+        <Button @click="handleLogout">Log Out</Button>
+    </div>
+    <div v-else class="flex flex-col">
+        <h1>Login</h1>
+        <input type="text" v-model="username" placeholder="Username" @keyup.enter="handleLogin" />
+        <input type="password" v-model="password" placeholder="Password" @keyup.enter="handleLogin" />
+        <Button @click="handleLogin">Log In</Button>
+    </div>
+</template>