fix(config): correct Settings.data_dir default from Path("data") to Path.home() / ".cleveragents"

The Settings class had data_dir defaulting to Path("data") — a relative
path — but the specification requires the default data directory to be
~/.cleveragents. This inconsistency caused any code reading Settings().data_dir
without setting CLEVERAGENTS_DATA_DIR to use a relative 'data/' directory
instead of the spec-required ~/.cleveragents, affecting log storage, database
location, cache, backups, and all persistent state.

Changes:
- Fix data_dir default_factory from Path("data") to Path.home() / ".cleveragents"
- Add Behave scenario: 'data_dir default is the spec-required home directory path'
- Add Behave scenario: 'data_dir env var override takes precedence over default'
- Add step definition: 'the data directory should equal the home cleveragents path'

Settings.data_dir is now consistent with ConfigService core.data-dir default
(~/.cleveragents). The CLEVERAGENTS_DATA_DIR env var override continues to work.

ISSUES CLOSED: #2851

features/steps/settings_steps.py

@@ -104,6 +104,15 @@ def step_check_log_dir_contains(context, substring):
     assert substring in str(context.settings.log_dir)
 
 
+@then("the data directory should equal the home cleveragents path")
+def step_check_data_dir_home_cleveragents(context):
+    """Check that data_dir defaults to Path.home() / '.cleveragents'."""
+    expected = Path.home() / ".cleveragents"
+    assert context.settings.data_dir == expected, (
+        f"Expected data_dir={expected!r}, got {context.settings.data_dir!r}"
+    )
+
+
 @then('the data directory should be "{expected}"')
 def step_check_data_dir(context, expected):
     """Check the data directory."""