feat: add Caddy configuration and update Dockerfile for proper working directory

caddy/Caddyfile

@@ -0,0 +1,4 @@
+mc.neody.ad.jp {
+    root /srv
+    file_server
+}

caddy/Dockerfile

@@ -10,7 +10,7 @@ RUN bun run build
 
 FROM caddy:latest
 
-WORKDIR /app
+WORKDIR /srv
 
-COPY --from=builder /app/out ./
+COPY caddy/Caddyfile /etc/caddy/Caddyfile
-COPY caddy/Caddyfile /etc/caddy/Caddyfile
+COPY --from=builder /app/out ./