fix(reddit): install rdt-cli from GitHub source pinned to 0.4.2 (#326)

PyPI still only has rdt-cli 0.4.1 while the doctor hint required >=0.4.2, so the suggested install command always failed. Installs from the upstream GitHub repo pinned to the 0.4.2 commit instead, and syncs all four docs that still taught the PyPI path. Verified locally: clean-venv install from the pinned source yields rdt 0.4.2 and rdt status works. 86 tests pass. Fixes #294.

tests/test_channels.py

@@ -654,6 +654,8 @@ class TestRedditChannel:
         assert status == "off"
         assert "rdt-cli" in msg
         assert "public-clis/rdt-cli" in msg
+        assert "git+https://github.com/public-clis/rdt-cli.git" in msg
+        assert "rdt-cli>=0.4.2" not in msg
 
     def test_reports_ok_when_authenticated(self, monkeypatch):
         monkeypatch.setattr(shutil, "which", lambda _: "/usr/local/bin/rdt")