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/404.vue

@@ -0,0 +1,13 @@
+<template>
+    <main class="flex flex-col items-center">
+        <div
+            class="a4page-portrait items-center bdr-1 flex flex-col relative overflow-scroll"
+        >
+            <h1>404</h1>
+            <RouterLink to="/" class="bdr-2">
+                <img src="/img/memes/epic.jpeg" />
+            </RouterLink>
+            <h1>Click her, she will take you home</h1>
+        </div>
+    </main>
+</template>