feat: Implement latency profiling and guardrails for performance monitoring

- Added synthetic latency profiler scenarios and CLI scripts for baseline generation and regression checks.
- Introduced latency baseline and threshold artifacts for CI enforcement.
- Enhanced CI workflow with latency guardrail checks.
- Updated documentation to include latency profiling commands and performance metrics.
- Added unit tests for latency guardrail evaluation.

tests/unit/test_settings_validation.py

@@ -11,7 +11,11 @@ def test_dashboard_auth_requires_both_fields() -> None:
 
 def test_kraken_api_auth_requires_key_and_secret() -> None:
     with pytest.raises(ValidationError):
-        Settings(_env_file=None, KRAKEN_API_KEY="key-only")
+        Settings(
+            _env_file=None,
+            KRAKEN_API_KEY="key-only",
+            KRAKEN_API_SECRET="",
+        )
 
 
 def test_kraken_permissions_require_query_and_trade() -> None: