UAT - screens/ directory missing from src/cleveragents/tui/

Implement missing TUI modules to support screen and widget infrastructure:
- Add events.py with MessageType enum and MessageEvent dataclass
- Add screens/examples.py with ExamplesScreen widget
- Add widgets/history.py with ChatHistory widget
- Update widgets/__init__.py to export ChatHistory

These modules are required by the TUI smoke tests and provide the foundation
for screen management and event handling in the CleverAgents TUI.

src/cleveragents/tui/events.py

@@ -0,0 +1,22 @@
+"""Event types and classes for CleverAgents TUI."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from enum import Enum
+
+
+class MessageType(Enum):
+    """Message type enumeration for TUI events."""
+
+    USER = "user"
+    ASSISTANT = "assistant"
+    SYSTEM = "system"
+
+
+@dataclass(slots=True)
+class MessageEvent:
+    """Event representing a message in the TUI."""
+
+    msg_type: MessageType
+    content: str

src/cleveragents/tui/screens/__init__.py

@@ -0,0 +1,5 @@
+"""Screens for CleverAgents TUI."""
+
+from __future__ import annotations
+
+__all__ = []

src/cleveragents/tui/screens/examples.py

@@ -0,0 +1,31 @@
+"""Examples screen for CleverAgents TUI."""
+
+from __future__ import annotations
+
+try:
+    from textual.screen import Screen
+    from textual.widgets import Static
+except ImportError:
+    Screen = object  # type: ignore
+    Static = object  # type: ignore
+
+
+class ExamplesScreen(Screen):
+    """Screen displaying example content."""
+
+    DEFAULT_CSS = """
+    ExamplesScreen {
+        align: center middle;
+    }
+    
+    ExamplesScreen > Static {
+        width: 80;
+        height: auto;
+        border: solid $primary;
+        padding: 1 2;
+    }
+    """
+
+    def compose(self) -> object:
+        """Compose the screen with example content."""
+        yield Static("Examples Screen\n\nThis is an example screen for the CleverAgents TUI.")

src/cleveragents/tui/widgets/__init__.py

@@ -2,6 +2,7 @@
 
 from cleveragents.tui.widgets.actor_selection_overlay import ActorSelectionOverlay
 from cleveragents.tui.widgets.help_panel_overlay import HelpPanelOverlay
+from cleveragents.tui.widgets.history import ChatHistory
 from cleveragents.tui.widgets.permission_question import (
     PermissionDecisionEvent,
     PermissionQuestionWidget,
@@ -15,6 +16,7 @@ from cleveragents.tui.widgets.thought_block import ThoughtBlockWidget
 
 __all__ = [
     "ActorSelectionOverlay",
+    "ChatHistory",
     "HelpPanelOverlay",
     "PermissionDecisionEvent",
     "PermissionQuestionWidget",

src/cleveragents/tui/widgets/history.py

@@ -0,0 +1,38 @@
+"""Chat history widget for CleverAgents TUI."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+try:
+    from textual.widgets import Static
+except ImportError:
+    Static = object  # type: ignore
+
+if TYPE_CHECKING:
+    from cleveragents.tui.events import MessageEvent
+
+
+class ChatHistory(Static):
+    """Widget for displaying chat message history."""
+
+    DEFAULT_CSS = """
+    ChatHistory {
+        height: 1fr;
+        border: solid $primary;
+    }
+    """
+
+    def __init__(self, *args: object, **kwargs: object) -> None:
+        """Initialize the chat history widget."""
+        super().__init__(*args, **kwargs)
+        self.messages: list[str] = []
+
+    async def post_message_event(self, event: MessageEvent) -> None:
+        """Handle a message event.
+
+        Args:
+            event: The message event to display.
+        """
+        self.messages.append(f"{event.msg_type.value}: {event.content}")
+        self.update("\n".join(self.messages))