Add daemon lifecycle subcommands: start, stop, reload, status

Implement CLI subcommands for managing telemt as a daemon:

- `start [config.toml]` - Start as background daemon (implies --daemon)
- `stop` - Stop running daemon by sending SIGTERM
- `reload` - Reload configuration by sending SIGHUP
- `status` - Check if daemon is running via PID file

Subcommands use the PID file (default /var/run/telemt.pid) to locate
the running daemon. Stop command waits up to 10 seconds for graceful
shutdown. Status cleans up stale PID files automatically.

Updated help text with subcommand documentation and usage examples.
Exit codes follow Unix convention: 0 for success, 1 for not running
or error.

Signed-off-by: Vladimir Krivopalov <argenet@yandex.ru>

src/main.rs

@@ -30,11 +30,18 @@ mod transport;
 mod util;
 
 fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
+    let args: Vec<String> = std::env::args().skip(1).collect();
+    let cmd = cli::parse_command(&args);
+
+    // Handle subcommands that don't need the server (stop, reload, status, init)
+    if let Some(exit_code) = cli::execute_subcommand(&cmd) {
+        std::process::exit(exit_code);
+    }
+
     // On Unix, handle daemonization before starting tokio runtime
     #[cfg(unix)]
     {
-        let args: Vec<String> = std::env::args().skip(1).collect();
-        let daemon_opts = cli::parse_daemon_args(&args);
+        let daemon_opts = cmd.daemon_opts;
 
         // Daemonize if requested (must happen before tokio runtime starts)
         if daemon_opts.should_daemonize() {