feat(docker): add caddy reverse proxy assets

docker/docker-compose.proxy.yml

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+# =============================================================================
+# SurfSense — Optional Caddy reverse-proxy overlay
+# =============================================================================
+# Usage (from docker/):
+#   PROXY_HTTP_PORT=8080 SURFSENSE_PUBLIC_URL=http://localhost:8080 \
+#     docker compose -f docker-compose.yml -f docker-compose.proxy.yml up -d
+#
+# This overlay is for validation and custom deployments. The production
+# docker-compose.yml includes Caddy by default.
+# =============================================================================
+
+services:
+  backend:
+    ports:
+      - "${BACKEND_PORT:-8929}:8000"
+
+  zero-cache:
+    ports:
+      - "${ZERO_CACHE_PORT:-5929}:4848"
+
+  frontend:
+    ports:
+      - "${FRONTEND_PORT:-3929}:3000"
+
+  proxy:
+    image: caddy:2-alpine
+    restart: unless-stopped
+    ports:
+      - "${PROXY_HTTP_PORT:-8080}:80"
+      - "${PROXY_HTTPS_PORT:-8443}:443"
+    volumes:
+      - ./proxy/Caddyfile:/etc/caddy/Caddyfile:ro
+      - caddy_data:/data
+      - caddy_config:/config
+    environment:
+      SURFSENSE_SITE_ADDRESS: ${SURFSENSE_SITE_ADDRESS:-:80}
+      CERT_EMAIL: ${CERT_EMAIL:-}
+      CERT_ACME_CA: ${CERT_ACME_CA:-https://acme-v02.api.letsencrypt.org/directory}
+      CERT_ACME_DNS: ${CERT_ACME_DNS:-}
+      TRUSTED_PROXIES: ${TRUSTED_PROXIES:-0.0.0.0/0}
+      SURFSENSE_MAX_BODY_SIZE: ${SURFSENSE_MAX_BODY_SIZE:-5GB}
+    depends_on:
+      frontend:
+        condition: service_started
+      backend:
+        condition: service_healthy
+      zero-cache:
+        condition: service_healthy
+
+volumes:
+  caddy_data:
+    name: surfsense-caddy-data
+  caddy_config:
+    name: surfsense-caddy-config

docker/proxy/Caddyfile

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+{
+	# Optional ACME/global settings. These are harmless in the default :80
+	# localhost mode and become active when SURFSENSE_SITE_ADDRESS is a domain.
+	{$CERT_EMAIL}
+	acme_ca {$CERT_ACME_CA:https://acme-v02.api.letsencrypt.org/directory}
+	{$CERT_ACME_DNS}
+	servers {
+		client_ip_headers X-Forwarded-For X-Real-IP
+		trusted_proxies static {$TRUSTED_PROXIES:0.0.0.0/0}
+	}
+}
+
+(surfsense_proxy) {
+	request_body {
+		max_size {$SURFSENSE_MAX_BODY_SIZE:5GB}
+	}
+
+	# Backend auth routes (FastAPI Users + OAuth helpers).
+	reverse_proxy /auth/* backend:8000
+
+	# Backend REST, streaming, connector OAuth, and messaging gateway endpoints.
+	# FastAPI already serves /api/v1, so the path is forwarded unchanged.
+	reverse_proxy /api/v1/* backend:8000
+
+	# Zero accepts a single path-component base URL (Zero >= 0.6).
+	# Preserve /zero so browser cacheURL can be ${SURFSENSE_PUBLIC_URL}/zero.
+	reverse_proxy /zero/* zero-cache:4848
+
+	# Next.js app and frontend-owned API routes:
+	# /api/zero/*, /api/search, /api/contact, etc.
+	reverse_proxy /* frontend:3000
+}
+
+{$SURFSENSE_SITE_ADDRESS::80} {
+	import surfsense_proxy
+}

docker/proxy/Dockerfile

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+FROM caddy:2-builder-alpine AS builder
+
+RUN xcaddy build \
+	--with github.com/caddy-dns/cloudflare \
+	--with github.com/caddy-dns/digitalocean
+
+FROM caddy:2-alpine
+
+COPY --from=builder /usr/bin/caddy /usr/bin/caddy
+COPY Caddyfile /etc/caddy/Caddyfile