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

pyproject.toml

@@ -76,6 +76,8 @@ addopts = [
 markers = [
     "benchmark: marks tests as performance benchmarks (may be slow)",
     "e2e: marks tests as end-to-end tests (require network/display)",
+    "integration: marks tests as integration tests (require external services)",
+    "ntfy: marks tests that require ntfy service",
 ]
 filterwarnings = [
     "ignore::DeprecationWarning",