[codex] refactor shared strategy catalog contract

[Pigbibi]

What changed

• add a shared strategy catalog contract in QuantPlatformKit
• add shared platform policy helpers for enabled/default/rollback strategy resolution
• keep the old resolver APIs in place for compatibility

Why

• strategy metadata and platform policy should live behind a neutral shared contract
• downstream repos can then stop re-implementing registry glue and stop depending on US equity helpers for generic behavior

Impact

• no runtime behavior change intended
• this is the shared base for the follow-up UES/Crypto/platform PRs

Validation

• python3 -m py_compile src/quant_platform_kit/common/strategies.py src/quant_platform_kit/__init__.py tests/test_strategies.py
• python3 -m ruff check src/quant_platform_kit/common/strategies.py src/quant_platform_kit/__init__.py tests/test_strategies.py
• PYTHONPATH=src ... pytest tests/test_strategies.py