feat: add UserMessage widget and UI backend selection during onboarding

- Introduced UserMessage widget for displaying user input with a styled prompt.
- Updated onboarding steps to include UI backend selection (Rich CLI or Textual TUI).
- Modified EvoScientistConfig to store selected UI backend.
- Enhanced configuration handling to support UI backend environment variable.
- Updated README with new UI backend options and commands.
- Added tests for new UI backend functionality and UserMessage widget.
- Removed obsolete test files and ensured existing tests are updated accordingly.

tests/test_cli_tui_dispatch.py

@@ -0,0 +1,53 @@
+"""Tests for CLI interactive UI backend dispatch."""
+
+from EvoScientist.cli.interactive import cmd_interactive
+
+
+def test_cmd_interactive_dispatches_to_textual(monkeypatch):
+    captured: dict[str, object] = {}
+
+    def _fake_resolve_ui_backend(value, *, warn_fallback=False):  # noqa: ANN001
+        captured["resolved_input"] = value
+        captured["warn_fallback"] = warn_fallback
+        return "textual"
+
+    def _fake_run_textual_interactive(**kwargs):  # noqa: ANN003
+        captured["kwargs"] = kwargs
+
+    monkeypatch.setattr(
+        "EvoScientist.cli.interactive.resolve_ui_backend",
+        _fake_resolve_ui_backend,
+    )
+    monkeypatch.setattr(
+        "EvoScientist.cli.interactive.run_textual_interactive",
+        _fake_run_textual_interactive,
+    )
+
+    cmd_interactive(
+        show_thinking=True,
+        channel_send_thinking=True,
+        workspace_dir="/tmp/workspace",
+        workspace_fixed=True,
+        mode="daemon",
+        model="demo-model",
+        provider="demo-provider",
+        run_name="demo-run",
+        thread_id="thread-1",
+        ui_backend="textual",
+    )
+
+    assert captured["resolved_input"] == "textual"
+    assert captured["warn_fallback"] is True
+
+    kwargs = captured["kwargs"]
+    assert isinstance(kwargs, dict)
+    assert kwargs["workspace_dir"] == "/tmp/workspace"
+    assert kwargs["workspace_fixed"] is True
+    assert kwargs["mode"] == "daemon"
+    assert kwargs["model"] == "demo-model"
+    assert kwargs["provider"] == "demo-provider"
+    assert kwargs["run_name"] == "demo-run"
+    assert kwargs["thread_id"] == "thread-1"
+    assert kwargs["channel_send_thinking"] is True
+    assert callable(kwargs["load_agent"])
+    assert callable(kwargs["create_session_workspace"])