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>

docker-compose.dev.yml

@@ -1,4 +1,11 @@
 services:
+    vue:
+        command: ["npm", "run", "dev"]
+        volumes:
+            - ./vue:/app
+            - /app/node_modules
+        environment:
+            - NODE_ENV=development
     nginx:
         environment:
             - DEV_MODE=true