refactor(tests): extract onboard logic tests to dedicated module

- Move onboard-related tests from test_commands.py and test_config_migration.py
  to new test_onboard_logic.py for better organization
- Add comprehensive unit tests for:
  - _merge_missing_defaults recursive config merging
  - _get_field_type_info type extraction
  - _get_field_display_name human-readable name generation
  - _format_value display formatting
  - sync_workspace_templates file synchronization
- Remove unused dev dependencies (matrix-nio, mistune, nh3) from pyproject.toml

tests/test_commands.py

@@ -1,6 +1,5 @@
 import json
 import re
-import shutil
 from pathlib import Path
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -13,12 +12,6 @@ from nanobot.providers.litellm_provider import LiteLLMProvider
 from nanobot.providers.openai_codex_provider import _strip_model_prefix
 from nanobot.providers.registry import find_by_model
 
-
-def _strip_ansi(text):
-    """Remove ANSI escape codes from text."""
-    ansi_escape = re.compile(r'\x1b\[[0-9;]*m')
-    return ansi_escape.sub('', text)
-
 runner = CliRunner()
 
 
@@ -26,6 +19,11 @@ class _StopGateway(RuntimeError):
     pass
 
 
+import shutil
+
+import pytest
+
+
 @pytest.fixture
 def mock_paths():
     """Mock config/workspace paths for test isolation."""
@@ -117,6 +115,12 @@ def test_onboard_existing_workspace_safe_create(mock_paths):
     assert (workspace_dir / "AGENTS.md").exists()
 
 
+def _strip_ansi(text):
+    """Remove ANSI escape codes from text."""
+    ansi_escape = re.compile(r'\x1b\[[0-9;]*m')
+    return ansi_escape.sub('', text)
+
+
 def test_onboard_help_shows_workspace_and_config_options():
     result = runner.invoke(app, ["onboard", "--help"])