feat(settings): add update_ssh action with confirm=True guard

Enables/disables SSH and sets port via updateSshSettings mutation
(UpdateSshInput: enabled: Boolean!, port: Int!). Changing SSH config
can lock users out of the server — requires confirm=True.

- Add update_ssh to MUTATIONS, DESTRUCTIVE_ACTIONS, SETTINGS_ACTIONS
- Add ssh_enabled/ssh_port parameters to unraid_settings
- Add TestSshSettings class (4 tests: require ssh_enabled, require ssh_port, success, disable+verify vars)
- Update safety test KNOWN_DESTRUCTIVE + _DESTRUCTIVE_TEST_CASES + positive confirm test
- Update schema completeness test

757 tests passing

tests/schema/test_query_validation.py

@@ -765,6 +765,7 @@ class TestSettingsMutations:
             "connect_sign_out",
             "setup_remote_access",
             "enable_dynamic_remote_access",
+            "update_ssh",
         }
         assert set(MUTATIONS.keys()) == expected