docs: fix the claude mcp add form, pin the package index, document known limitations

The --env option swallowed the server name, so the stdio command is reordered. uvx now always
names the project registry because the package name is not registered on public PyPI.
README gains a Known limitations section, the READ_ONLY wording is corrected, packaging.md
warns about --extra-index-url and the Le Chat admin requirement is mentioned.

tests/test_setup.py

@@ -173,8 +173,14 @@ def test_printed_configs(httpx_mock: HTTPXMock, capsys: pytest.CaptureFixture[st
     mock_create(httpx_mock)
     assert run_setup() == 0
     out = capsys.readouterr().out
-    assert f"--env GITEA_URL={GITEA} --env GITEA_TOKEN=<your-gitea-token>" in out
-    assert "uvx aegis-gitea-mcp" in out
+    index = "https://git.hiddenden.cafe/api/packages/Hiddenden/pypi/simple/"
+    assert (
+        f"claude mcp add --env GITEA_URL={GITEA} --env GITEA_TOKEN=<your-gitea-token> "
+        f"--transport stdio aegis-gitea -- uvx --index {index} aegis-gitea-mcp"
+    ) in out
+    # The bare name would resolve from public PyPI, where it is not registered.
+    assert "uvx aegis-gitea-mcp" not in out
+    assert f'"--index",\n        "{index}"' in out
     assert '"mcpServers"' in out
     assert (
         f"claude mcp add --transport http aegis-gitea {PUBLIC}/mcp "