Allow IBKR execution to use close price fallbacks

[Pigbibi]

Summary

• allow live execution to use strategy-provided close-price fallbacks when IBKR quote snapshots are missing
• expose recent historical close fallbacks for value/market-history runtimes, including the TQQQ slot A path
• keep dry-run snapshot wording separate from live execution fallback wording

Validation

• PYTHONPATH=/home/ubuntu/Projects/QuantPlatformKit/src:/home/ubuntu/Projects/UsEquityStrategies/src PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/python -m pytest -q tests/test_execution_service.py tests/test_strategy_runtime.py tests/test_rebalance_service.py
• .venv/bin/python -m ruff check application/execution_service.py strategy_runtime.py notifications/renderers.py notifications/telegram.py tests/test_execution_service.py tests/test_strategy_runtime.py tests/test_rebalance_service.py
• git diff --check

Ops

• updated Cloud Scheduler slot B precheck/probe to the monthly execution window (1-7).