feat(pipeline): add unified pipeline architecture with Stage abstraction

- Add engine/pipeline/ module with Stage ABC, PipelineContext, PipelineParams
- Stage provides unified interface for sources, effects, displays, cameras
- Pipeline class handles DAG-based execution with dependency resolution
- PipelinePreset for pre-configured pipelines (demo, poetry, pipeline, etc.)
- Add PipelineParams as params layer for animation-driven config
- Add StageRegistry for unified stage registration
- Add sources_v2.py with DataSource.is_dynamic property
- Add animation.py with Preset and AnimationController
- Skip ntfy integration tests by default (require -m integration)
- Skip e2e tests by default (require -m e2e)
- Update pipeline.py with comprehensive introspection methods

tests/test_ntfy_integration.py

@@ -6,7 +6,11 @@ import json
 import time
 import urllib.request
 
+import pytest
 
+
+@pytest.mark.integration
+@pytest.mark.ntfy
 class TestNtfyTopics:
     def test_cc_cmd_topic_exists_and_writable(self):
         """Verify C&C CMD topic exists and accepts messages."""