feat: expose browser control via ServiceLink RPC

- Add the ServiceLink submodule and register it in .gitmodules.
- Add a link-serve command that exposes selected browser-cli commands over an HTTP /rpc endpoint.
- Require bearer-token authentication by default, with explicit insecure opt-in for trusted loopback/local deployments.
- Allow the existing serve daemon to run the ServiceLink RPC endpoint alongside the native TCP remote server.

browser_cli/commands/serve.py

@@ -45,9 +45,32 @@ __all__ = [
     default=False,
     help="Disable response compression / msgpack even for clients that support it.",
 )
+@click.option(
+    "--rpc",
+    is_flag=True,
+    default=False,
+    help="Also expose a ServiceLink HTTP /rpc endpoint (for mesh nodes) in the same process.",
+)
+@click.option("--rpc-port", default=8770, show_default=True, type=int, help="Port for the /rpc endpoint (with --rpc).")
+@click.option(
+    "--rpc-token",
+    default=None,
+    metavar="SECRET",
+    help="Bearer token required on /rpc (with --rpc).",
+)
+@click.option(
+    "--rpc-insecure",
+    is_flag=True,
+    default=False,
+    help="Allow --rpc with no token (DANGEROUS: full browser control to anyone who can reach the port).",
+)
 @click.pass_context
-def cmd_serve(ctx, host, port, no_auth, auth_keys_file, no_compress):
-    """Expose this browser over TCP so remote hosts can control it."""
+def cmd_serve(ctx, host, port, no_auth, auth_keys_file, no_compress, rpc, rpc_port, rpc_token, rpc_insecure):
+    """Expose this browser over TCP so remote hosts can control it.
+
+    With --rpc, additionally serve the ServiceLink mesh over HTTP /rpc on
+    --rpc-port, so the native TCP protocol and the node mesh share one daemon.
+    """
     profile = ctx.obj.get("browser") if ctx.obj else None
     compress = not no_compress
 
@@ -61,16 +84,40 @@ def cmd_serve(ctx, host, port, no_auth, auth_keys_file, no_compress):
     if auth_keys_path is False:
         sys.exit(1)
 
+    if rpc and not rpc_token and not rpc_insecure:
+        console.print(
+            "[red]Error:[/red] --rpc requires --rpc-token (this endpoint can control your "
+            "browser and read its cookies). Use --rpc-insecure to override on a trusted host."
+        )
+        sys.exit(1)
+
     _print_startup(host, port, profile, auth_keys_path, compress)
+    if rpc:
+        console.print(f"  Mesh:   [green]ServiceLink HTTP[/green] [cyan]{host}:{rpc_port}/rpc[/cyan]")
+        if not rpc_token:
+            console.print("[yellow]  /rpc auth disabled (--rpc-insecure)[/yellow]")
 
     try:
-        asyncio.run(_serve_async(host, port, profile, auth_keys_path, compress))
+        if rpc:
+            asyncio.run(_serve_with_rpc(host, port, profile, auth_keys_path, compress, rpc_port, rpc_token))
+        else:
+            asyncio.run(_serve_async(host, port, profile, auth_keys_path, compress))
     except OSError as e:
         console.print(f"[red]Cannot bind to {host}:{port}:[/red] {e}")
         sys.exit(1)
     except KeyboardInterrupt:
         console.print("[yellow]Stopped.[/yellow]")
 
+async def _serve_with_rpc(host, port, profile, auth_keys_path, compress, rpc_port, rpc_token):
+    """Run the native TCP server and the ServiceLink HTTP /rpc server together."""
+    from browser_cli.commands import link_serve
+
+    sl = link_serve._import_servicelink()
+    await asyncio.gather(
+        _serve_async(host, port, profile, auth_keys_path, compress),
+        link_serve._serve(sl, host, rpc_port, profile, rpc_token),
+    )
+
 def _resolve_auth_keys_path(auth_keys_file: str | None, no_auth: bool) -> Path | None | bool:
     if auth_keys_file:
         from browser_cli.auth import load_authorized_keys