Handle zero-equity Firstrade strategy runs

[Pigbibi]

Summary

• parse Firstrade account balances from broader total-equity field shapes and account-list totals
• preserve zero-equity account runs by no-executing weight-target decisions instead of raising during execution translation
• support Firstrade-style formatted money strings in account payload parsing

Tests

• uv run --no-project --with pytest --with pandas --with requests --with google-cloud-storage --with firstrade==0.0.38 python -m pytest tests/test_runtime_broker_adapters.py tests/test_firstrade_client.py tests/test_rebalance_service.py
• uv run --no-project --with ruff ruff check decision_mapper.py application/account_payload_utils.py application/firstrade_client.py application/runtime_broker_adapters.py tests/test_firstrade_client.py tests/test_runtime_broker_adapters.py tests/test_rebalance_service.py

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve explicit non-positive account equity

When Firstrade returns an authoritative non-positive total/account value, such as a margin-deficit balance formatted as ($50.00), _positive_or_none treats it as missing and falls through to cash/position fallbacks. If the positions endpoint still reports positive market values, the snapshot becomes positive and weight targets can be translated and executed instead of hitting the total_equity <= 0 no-execute guard. Only absent/unparseable totals should fall back; parsed <= 0 totals should be preserved so the execution block remains effective.

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