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>

.gitignore

@@ -9,8 +9,8 @@ gitea/config/app.ini
 gitea/data/*
 gitea-runner/data/*
 
-# Will add in future (webpack)
-nginx/vue/crates/
+# Rust build artifacts
+**/target/
 
 # Logs
 logs