fix(config): align Settings and alembic/env.py database_url defaults to spec-required ~/.cleveragents/cleveragents.db

- Fix Settings.database_url default from relative 'sqlite:///cleveragents.db'
  to absolute 'sqlite:////home/<user>/.cleveragents/cleveragents.db' using
  Path.home() / '.cleveragents' / 'cleveragents.db'
- Fix test_database_url default similarly to use ~/.cleveragents/cleveragents_test.db
- Fix alembic/env.py fallback default from Path.cwd() / '.cleveragents' / 'db.sqlite'
  to Path.home() / '.cleveragents' / 'cleveragents.db' (matching Settings)
- Both Settings and alembic/env.py now resolve to the same absolute path
- CLEVERAGENTS_DATABASE_URL env var override still works correctly in both
- Update coverage_boost_steps.py assertions to match new correct defaults
- Add 3 new Behave scenarios covering correct database_url default and env var override

ISSUES CLOSED: #2871

features/steps/settings_steps.py

@@ -650,3 +650,53 @@ def step_singleton_instances_should_be_different(context: Context) -> None:
 def step_singleton_environment_should_be(context: Context, expected: str) -> None:
     """Assert the latest singleton reflects the current environment value."""
     assert context.settings.environment == expected
+
+
+@given('"{key}" is not set')
+def step_env_var_not_set(context: Context, key: str) -> None:
+    """Ensure a specific environment variable is not set."""
+    os.environ.pop(key, None)
+    if not hasattr(context, "env_vars_to_clean"):
+        context.env_vars_to_clean = []
+    # Track it so teardown knows to clean it if it gets set later
+    context.env_vars_to_clean.append(key)
+
+
+@then('the database URL should point to "~/.cleveragents/cleveragents.db"')
+def step_database_url_points_to_home(context: Context) -> None:
+    """Verify the database URL resolves to the spec-required home directory path."""
+    expected_path = Path.home() / ".cleveragents" / "cleveragents.db"
+    url = context.settings.database_url
+    assert str(expected_path) in url, (
+        f"Expected database URL to contain '{expected_path}', got: {url}"
+    )
+
+
+@then('the database URL should start with "{prefix}"')
+def step_database_url_starts_with(context: Context, prefix: str) -> None:
+    """Verify the database URL starts with the given prefix."""
+    url = context.settings.database_url
+    assert url.startswith(prefix), (
+        f"Expected database URL to start with '{prefix}', got: {url}"
+    )
+
+
+@then('the database URL should contain "{substring}"')
+def step_database_url_contains(context: Context, substring: str) -> None:
+    """Verify the database URL contains the given substring."""
+    url = context.settings.database_url
+    assert substring in url, (
+        f"Expected database URL to contain '{substring}', got: {url}"
+    )
+
+
+@then("the database URL should be an absolute path")
+def step_database_url_is_absolute(context: Context) -> None:
+    """Verify the database URL uses an absolute path (not relative)."""
+    url = context.settings.database_url
+    # For SQLite URLs: sqlite:////absolute/path or sqlite:///relative
+    # Absolute paths have 4 slashes: sqlite:////home/...
+    # Relative paths have 3 slashes: sqlite:///relative
+    assert url.startswith("sqlite:////") or (
+        url.startswith("sqlite:///") and Path(url[len("sqlite:///") :]).is_absolute()
+    ), f"Expected database URL to use an absolute path, got: {url}"