Refactor/cli command manager (#178)

* feat(cli): migrate command handling to CommandManager and enhance UI interactions

* feat(cli): add /clear and /help commands to enhance user experience

* feat(cli): implement /new and /resume commands with interactive session management

* Refactor MCP and Skills Command Handling

- Moved the interactive picker style to a centralized widget for consistency across MCP and Skills commands.
- Updated the MCP command to remove the old command dispatch logic, delegating to the new InstallMCPCommand.
- Enhanced the Skills command to utilize a new interactive picker for skill selection, improving user experience.
- Implemented cancellation handling in the picker to differentiate between user cancellations and empty selections.
- Added comprehensive tests for the new command structures and picker functionalities to ensure reliability.

* refactor(cli): streamline CommandManager dispatch and remove deprecated command set

* refactor(cli): enhance error handling and state management in ChannelCommand and RichCLICommandUI

* refactor(cli): update lifecycle callback terminology and improve async prompt handling in RichCLICommandUI

* refactor(cli): enhance SlashCommandCompleter to dynamically fetch workspace directory for autocompletion

* refactor(cli): unify quit handling in RichCLICommandUI with shared _stop helper

* refactor(cli): remove hardcoded slash commands and utilize command manager for dynamic completion

* refactor(cli): update MCP and skills command files for improved clarity and organization

* refactor(mcp_ui): remove unnecessary newline in _show_mcp_config function

tests/test_new_command.py

@@ -0,0 +1,36 @@
+"""Tests for the /new command."""
+
+from unittest.mock import MagicMock
+
+from tests.conftest import run_async as _run
+
+
+class TestNewCommand:
+    def test_execute_calls_start_new_session(self):
+        from EvoScientist.commands.base import CommandContext
+        from EvoScientist.commands.implementation.session import NewCommand
+
+        ui = MagicMock()
+        ctx = CommandContext(
+            agent=None,
+            thread_id="old-tid",
+            ui=ui,
+            workspace_dir="/old/ws",
+        )
+        _run(NewCommand().execute(ctx, []))
+        ui.start_new_session.assert_called_once()
+
+    def test_requires_agent_false(self):
+        from EvoScientist.commands.implementation.session import NewCommand
+
+        assert NewCommand().requires_agent is False
+
+    def test_no_agent_access(self):
+        """Command body must not touch ctx.agent (it's still loading)."""
+        from EvoScientist.commands.base import CommandContext
+        from EvoScientist.commands.implementation.session import NewCommand
+
+        ui = MagicMock()
+        ctx = CommandContext(agent=None, thread_id="tid", ui=ui)
+        # No AttributeError even though ctx.agent is None
+        _run(NewCommand().execute(ctx, []))