Add CF_CONFIG env var for simpler Docker workflow

Config search order is now:
1. --config CLI option
2. CF_CONFIG environment variable
3. ./compose-farm.yaml
4. ~/.config/compose-farm/compose-farm.yaml

Docker workflow simplified: mount compose_dir once, set CF_CONFIG
to config file within it. No more symlink issues or multiple mounts.

docker-compose.yml

@@ -3,9 +3,9 @@ services:
     image: ghcr.io/basnijholt/compose-farm:latest
     volumes:
       - ${SSH_AUTH_SOCK}:/ssh-agent:ro
-      # Config directory (must contain compose-farm.yaml, stores state.yaml)
-      - ${CF_CONFIG_DIR:-~/.config/compose-farm}:/root/.config/compose-farm
-      # Compose directory (mount at same path so compose_dir in config works)
-      - ${CF_COMPOSE_DIR:-/opt/compose}:${CF_COMPOSE_DIR:-/opt/compose}:ro
+      # Compose directory (contains compose files AND compose-farm.yaml config)
+      - ${CF_COMPOSE_DIR:-/opt/compose}:${CF_COMPOSE_DIR:-/opt/compose}
     environment:
       - SSH_AUTH_SOCK=/ssh-agent
+      # Config file path (state stored alongside it)
+      - CF_CONFIG=${CF_COMPOSE_DIR:-/opt/compose}/compose-farm.yaml

src/compose_farm/config.py

@@ -148,9 +148,10 @@ def load_config(path: Path | None = None) -> Config:
     """Load configuration from YAML file.
 
     Search order:
-    1. Explicit path if provided
-    2. ./compose-farm.yaml
-    3. $XDG_CONFIG_HOME/compose-farm/compose-farm.yaml (defaults to ~/.config)
+    1. Explicit path if provided via --config
+    2. CF_CONFIG environment variable
+    3. ./compose-farm.yaml
+    4. $XDG_CONFIG_HOME/compose-farm/compose-farm.yaml (defaults to ~/.config)
     """
     search_paths = [
         Path("compose-farm.yaml"),
@@ -159,6 +160,8 @@ def load_config(path: Path | None = None) -> Config:
 
     if path:
         config_path = path
+    elif env_path := os.environ.get("CF_CONFIG"):
+        config_path = Path(env_path)
     else:
         config_path = None
         for p in search_paths: