feat: expose all types through stable public API (#69)

* feat: expose all types through stable public API with union aliases

- Add 134 missing base types to stable.py exports (202 total)
- Add 4 semantic aliases for AuthorizedAgents discriminated union variants
- Add 4 union type aliases (Deployment, Destination, AuthorizedAgent, PublisherProperties)
- Update types/__init__.py to export all types from stable and aliases modules
- Fix test imports to use _generated instead of generated_poc
- All 295 tests passing

Users can now import all types from adcp.types or adcp package without accessing internal modules. Union type aliases simplify type hints for discriminated unions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: resolve linting errors in type exports

- Run ruff --fix to auto-format import statements
- Add GeneratedTaskStatus to __all__ exports

All 295 tests passing. Fixes CI linting failures.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

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Co-authored-by: Claude <noreply@anthropic.com>

Author: bokelley