feat: add Caddy reverse proxy with auto HTTPS for LAN access and auto-derive WebSocket URL (#863)

* feat: add Caddy reverse proxy with auto HTTPS for LAN access and auto-derive WebSocket URL

Add a Caddy service to docker-compose.standalone.yml that provides automatic
HTTPS with local certificates, enabling secure access to both the frontend
and API from the local network through a single entrypoint.

Backend changes:
- Add ROOT_PATH setting to FastAPI so the API can be served under /api prefix
- Route frontend and API (/server-api) through Caddy reverse proxy

Frontend changes:
- Support WEBSOCKET_URL=auto to derive the WebSocket URL from API_URL
  automatically, using the page protocol (http→ws, https→wss) and host
- Make WEBSOCKET_URL env var optional instead of required

* style: pre-commit

* fix: make standalone compose self-contained (drop !reset dependency)

docker-compose.standalone.yml used !reset YAML tags to clear
network_mode and volumes from the base compose. !reset requires
Compose v2.24+ and breaks on Colima + brew-installed compose.

Rewrite as a fully self-contained file with all services defined
directly (server, worker, beat, redis, postgres, web, garage, cpu,
gpu-nvidia, ollama, ollama-cpu). No longer overlays docker-compose.yml.

Update setup-standalone.sh compose_cmd() to use only the standalone
file instead of both files.

* fix: update standalone docs to match self-contained compose usage

---------

Co-authored-by: Igor Loskutov <igor.loskutoff@gmail.com>

docs/docs/installation/setup-standalone.md

@@ -191,7 +191,7 @@ Standalone runs without authentication (`FEATURE_REQUIRE_LOGIN=false`, `AUTH_BAC
 
 1. In `www/.env.local`: set `FEATURE_REQUIRE_LOGIN=true`, uncomment `AUTHENTIK_ISSUER` and `AUTHENTIK_REFRESH_TOKEN_URL`
 2. In `server/.env`: set `AUTH_BACKEND=authentik` (or your backend), configure `AUTH_JWT_AUDIENCE`
-3. Restart: `docker compose -f docker-compose.yml -f docker-compose.standalone.yml up -d --force-recreate web server`
+3. Restart: `docker compose -f docker-compose.standalone.yml up -d --force-recreate web server`
 
 ## What's NOT covered