feat: externalize buttplug as separate nginx container

- Add Dockerfile.buttplug: builds Rust/WASM + TS, serves via nginx
- Add nginx.buttplug.conf: serves /dist and /wasm with correct MIME types
- Add .gitea/workflows/docker-build-buttplug.yml: path-filtered CI workflow
- Strip Rust toolchain and buttplug build from frontend Dockerfile
- Move buttplug to devDependencies (types only at build time)
- Remove vite-plugin-wasm from frontend (WASM now served by nginx)
- Add /buttplug proxy in vite.config (dev: localhost:8080)
- Add buttplug service to compose.yml
- Load buttplug dynamically in play page via runtime import
- Fix faq page: suppress no-unnecessary-state-wrap for reassigned SvelteSet

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nginx.buttplug.conf

@@ -0,0 +1,23 @@
+server {
+    listen 80;
+    server_name _;
+
+    root /usr/share/nginx/html;
+
+    # WASM MIME type
+    include /etc/nginx/mime.types;
+    types {
+        application/wasm wasm;
+    }
+
+    # Cache JS and WASM aggressively (content-addressed by build)
+    location ~* \.(js|wasm)$ {
+        add_header Cache-Control "public, max-age=31536000, immutable";
+        add_header Cross-Origin-Resource-Policy "cross-origin";
+        add_header Cross-Origin-Embedder-Policy "require-corp";
+    }
+
+    location / {
+        try_files $uri =404;
+    }
+}