feat(activity): multi-service config, make help default, install-cli

Bare make lists targets. make install-cli installs the activity tool via uv.
Named activity-core backends live in ~/.config/activity/services.json with
list/add/use/default/which; -s/--service selects one call without changing
the default; --activity-url is a one-shot override.

tests/test_review_cli.py

@@ -122,13 +122,13 @@ action:
     )
     code = main(
         [
+            "list",
             "--cwd",
             str(tmp_path),
             "--repo",
             "freedom-intelligence",
             "--format",
             "json",
-            "list",
         ]
     )
     assert code in (0, 2)
@@ -176,13 +176,13 @@ action:
     )
     code = main(
         [
+            "status",
             "--cwd",
             str(tmp_path),
             "--repo",
             "freedom-intelligence",
             "--state-dir",
             str(tmp_path / "state"),
-            "status",
             "--since",
             "week",
         ]