feat: replace Nginx with Caddy for automatic SSL management

- Add Caddyfile with automatic HTTPS configuration
- Add Dockerfile.caddy for frontend build with Caddy
- Update docker-compose.yml to use Caddy service
- Update DEPLOY.md with simplified deployment instructions

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

deploy/Caddyfile

@@ -0,0 +1,33 @@
+{
+    email your-email@example.com
+}
+
+your-domain.com {
+    # Mobile client (default)
+    handle {
+        root * /srv/mobile
+        try_files {path} /index.html
+        file_server
+    }
+
+    # Screen client
+    handle /screen/* {
+        root * /srv/screen
+        uri strip_prefix /screen
+        try_files {path} /index.html
+        file_server
+    }
+
+    # API proxy
+    handle /api/* {
+        reverse_proxy server:3000
+    }
+
+    # WebSocket proxy
+    handle /socket.io/* {
+        reverse_proxy server:3000
+    }
+
+    # Gzip compression
+    encode gzip
+}

deploy/Dockerfile.caddy

@@ -0,0 +1,32 @@
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+
+RUN npm install -g pnpm
+
+COPY pnpm-workspace.yaml package.json pnpm-lock.yaml ./
+COPY packages/shared ./packages/shared
+COPY packages/client-screen ./packages/client-screen
+COPY packages/client-mobile ./packages/client-mobile
+
+RUN pnpm install --frozen-lockfile
+
+WORKDIR /app/packages/shared
+RUN pnpm build
+
+WORKDIR /app/packages/client-screen
+RUN pnpm build
+
+WORKDIR /app/packages/client-mobile
+RUN pnpm build
+
+# Production stage - Caddy
+FROM caddy:2-alpine
+
+COPY --from=builder /app/packages/client-screen/dist /srv/screen
+COPY --from=builder /app/packages/client-mobile/dist /srv/mobile
+COPY deploy/Caddyfile /etc/caddy/Caddyfile
+
+EXPOSE 80 443
+
+CMD ["caddy", "run", "--config", "/etc/caddy/Caddyfile"]