Add Docsify docs server with nginx

Move docs into docs/ directory, add Docsify for markdown rendering.
Standalone Docker stack (nginx:alpine) on port 8090.
wiring.html served as native HTML with correct MIME type.

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

docker-compose.yml

@@ -0,0 +1,16 @@
+services:
+  docs:
+    image: nginx:alpine
+    container_name: smart-trainer-docs
+    restart: unless-stopped
+    mem_limit: 64m
+    ports:
+      - "8090:80"
+    volumes:
+      - ./docs:/usr/share/nginx/html:ro
+      - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
+    healthcheck:
+      test: ["CMD", "wget", "-q", "--spider", "http://localhost:80/"]
+      interval: 30s
+      timeout: 5s
+      retries: 3