Core & API:
- Introduced `@pipe.sub` decorator for declarative sub-pipeline registration.
- Refactored `Run` primitive to internal `_Run` to enforce decorator usage.
- Updated `Pipe.switch` to fully support strong typing and `_Stop` signals.
- Implemented explicit lifecycle hooks (`on_startup`, `on_shutdown`) management.

Visualization (Mermaid):
- Completely refactored visualization engine (`justpipe.visualization`).
- Introduced recursive AST building for full sub-pipeline expansion.
- Added support for visualizing lifecycle hooks with distinct shapes.
- Improved node shapes: 'procs' for map targets, asymmetric for hooks.
- Fixed various Mermaid syntax generation issues.

Quality & Maintenance:
- Fixed 160+ `mypy` type-checking errors across the entire codebase.
- Added comprehensive type annotations to all tests and scripts.
- Fixed `asyncio.run` usage in test suite for stability.
- Removed empty/unused examples and updated all documentation.
- Regenerated all example graphs to match the new visualization engine.