fix: remove incorrect port-in-use check for reverse tunnels

The `_is_port_in_use` bind check was wrong for `-R` tunnels: local_port is
the forward target (e.g. a Docker container), so it should be listening,
not free. Drop the check — autossh doesn't require the target to be
reachable at startup.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/autossh_mgr/process.py

@@ -2,7 +2,6 @@ import os
 import shlex
 import shutil
 import signal
-import socket
 import subprocess
 import time
 from dataclasses import dataclass
@@ -115,20 +114,9 @@ def build_autossh_cmd(tunnel: TunnelConfig) -> list[str]:
     return cmd
 
 
-def _is_port_in_use(port: int) -> bool:
-    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-        try:
-            s.bind(("127.0.0.1", port))
-            return False
-        except OSError:
-            return True
-
-
 def start_tunnel(config_dir: Path, tunnel: TunnelConfig) -> int:
     if not shutil.which("autossh"):
         raise click.ClickException("autossh not found. Install it first.")
-    if _is_port_in_use(tunnel.local_port):
-        raise click.ClickException(f"Port {tunnel.local_port} is already in use")
 
     log_path = config_dir / "logs" / f"{tunnel.name}.log"
     log_path.parent.mkdir(parents=True, exist_ok=True)