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/graphql.js

@@ -0,0 +1,7 @@
+import axios from "axios";
+
+export async function gql(query, variables = {}) {
+  const res = await axios.post("/api/graphql", { query, variables });
+  if (res.data.errors && !res.data.data) throw new Error(res.data.errors[0].message);
+  return res.data.data;
+}