[codex] rename tech pullback cash buffer profile

[Pigbibi]

What changed

• renamed the canonical strategy profile from cash_buffer_branch_default to tech_pullback_cash_buffer
• renamed the strategy, snapshot, feature snapshot generator, and related tests to match the new canonical name
• updated README and catalog metadata so the runtime-facing name and human-facing display name are consistent
• removed the old alias and added an explicit test that the legacy profile name is rejected

Why

cash_buffer_branch_default was an internal engineering name. tech_pullback_cash_buffer is easier to understand from the profile name alone and matches the strategy semantics much better.

Validation

• python3 -m py_compile src/us_equity_strategies/catalog.py src/us_equity_strategies/strategies/tech_pullback_cash_buffer.py src/us_equity_strategies/snapshots/tech_pullback_cash_buffer.py scripts/generate_tech_pullback_cash_buffer_feature_snapshot.py tests/test_catalog.py tests/test_platform_registry_support.py tests/test_tech_pullback_cash_buffer.py tests/test_tech_pullback_cash_buffer_feature_snapshot.py
• python3 -m ruff check src/us_equity_strategies/catalog.py src/us_equity_strategies/strategies/tech_pullback_cash_buffer.py src/us_equity_strategies/snapshots/tech_pullback_cash_buffer.py scripts/generate_tech_pullback_cash_buffer_feature_snapshot.py tests/test_catalog.py tests/test_platform_registry_support.py tests/test_tech_pullback_cash_buffer.py tests/test_tech_pullback_cash_buffer_feature_snapshot.py
• PYTHONPATH=/Users/lisiyi/Projects/UsEquityStrategies/src:/Users/lisiyi/Projects/QuantPlatformKit/src /Users/lisiyi/Projects/InteractiveBrokersPlatform/.venv/bin/python -m pytest tests/test_catalog.py tests/test_platform_registry_support.py tests/test_tech_pullback_cash_buffer.py tests/test_tech_pullback_cash_buffer_feature_snapshot.py