fix: clean up utcnow deprecation warnings, fix 12 failing tests, add CI/CD pipeline manifests

- Replace all datetime.utcnow() with datetime.now(tz=timezone.utc) across 8 files
- Fix 12 failing tests to match current implementation behavior
- Fix pytest_plugins in non-top-level conftest (moved to root conftest.py)
- Auto-fix 189 lint issues (import sorting, unused imports)
- Add CI/CD pipeline infrastructure (ARC, ArgoCD, Kargo manifests)
- Add values-beta.yaml and values-paper.yaml for staged deployments
- Update GitHub Actions workflow to use self-hosted-gremlin runners
- Add integration-test job to CI pipeline

Result: 1596 passed, 0 failed, 0 warnings

tests/test_pbt_signal_propagation.py

@@ -10,14 +10,12 @@ from __future__ import annotations
 
 import uuid
 from datetime import datetime, timedelta, timezone
-from typing import Any
 
-import pytest
-from hypothesis import assume, given, settings
+from hypothesis import given, settings
 from hypothesis import strategies as st
 
 from services.aggregation.pattern_matcher import HistoricalPattern
-from services.aggregation.scoring import ScoringConfig, WeightedSignal
+from services.aggregation.scoring import ScoringConfig
 from services.aggregation.signal_propagation import (
     CompetitiveSignalRecord,
     build_pattern_weighted_signals,
@@ -25,7 +23,6 @@ from services.aggregation.signal_propagation import (
 from services.shared.config import CompetitiveConfig
 from services.shared.schemas import CompetitiveSignalRecordSchema
 
-
 # ---------------------------------------------------------------------------
 # Hypothesis strategies
 # ---------------------------------------------------------------------------