core/tools: announce a remote shell instead of judging it

`ssh prod` runs no command this scan can resolve, and what is typed or piped
into the shell it opens never reaches any gate — `write_pty` and
`run_argv(stdin=…)` are both unchecked input. The tool description said nothing
about it, so the call looked like any other.

The hop is now reported even when no command follows
(`RemoteTarget.shell`), and the review announces it: `remote shell on 'prod'
(ssh with no command; its input is not checked)`. It is a soft confirm like the
other reviews (YOLO may skip it, an escalation behind a hop still may not) — the
client itself stays outside the denylist, since there is no program to name.

tests/test_tools/test_command_scan.py

@@ -171,11 +171,16 @@ def test_unwrap_remote_batch_mode() -> None:
 
 def test_unwrap_remote_client_alone() -> None:
     """A client with no command opens a remote shell: nothing to unwrap."""
-    for argv in (["ssh", "prod"], ["ssh", "-N", "prod"], ["ssh", "-G", "prod"], ["ssh"], ["mosh", "prod"]):
+    for argv in (["ssh", "prod"], ["ssh", "-N", "prod"], ["ssh", "-G", "prod"], ["mosh", "prod"]):
         scan = unwrap_command(argv)
         assert scan.wrappers == (), argv
         assert scan.base == argv[0], argv
-        assert scan.remote is None, argv
+        assert scan.remote is not None, argv
+        assert scan.remote.shell is True, argv
+        assert scan.remote.host == "prod", argv
+    # Without a destination there is no hop to announce.
+    for argv in (["ssh"], ["ssh", "-V"]):
+        assert unwrap_command(argv).remote is None, argv
 
 
 def test_unwrap_remote_command_still_reviews_what_runs() -> None: