refactor(maestro): wire --config flag through to maestro registry

`registry::run` now accepts an `Option<PathBuf>` config override so the
umbrella binary's `--config` flag (and its clap-bound `MAESTRO_CONFIG`
env var) reach the registry, mirroring how the daemon already consumed
the override.

crates/maestro-registry/src/run.rs

@@ -9,13 +9,14 @@ use std::path::PathBuf;
 use tokio::net::TcpListener;
 
 use crate::{
-    default_config_path, load_config, router, Registry, CONFIG_PATH_ENV, ENV_REGISTRY_BIND_ADDR,
-    ENV_TOKEN,
+    default_config_path, load_config, router, Registry, ENV_REGISTRY_BIND_ADDR, ENV_TOKEN,
 };
 
-pub async fn run() -> Result<(), Box<dyn Error>> {
-    let config_path: PathBuf = match std::env::var_os(CONFIG_PATH_ENV) {
-        Some(p) => PathBuf::from(p),
+/// Run the registry. `config_override` is the top-level `--config` flag from
+/// the umbrella binary (also populated from `$MAESTRO_CONFIG` by clap).
+pub async fn run(config_override: Option<PathBuf>) -> Result<(), Box<dyn Error>> {
+    let config_path: PathBuf = match config_override {
+        Some(p) => p,
         None => default_config_path()?,
     };
     let env_token = std::env::var(ENV_TOKEN).ok();

crates/maestro/src/main.rs

@@ -152,7 +152,7 @@ async fn dispatch(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
         #[cfg(feature = "daemon")]
         Command::Daemon { cmd } => maestro_daemon::cli::dispatch(cli.config, cmd).await?,
         #[cfg(feature = "registry")]
-        Command::Registry => maestro_registry::run().await?,
+        Command::Registry => maestro_registry::run(cli.config).await?,
     }
     Ok(())
 }