Apply small-account whole-share compatibility

[Pigbibi]

Applies the small-account whole-share compatibility layer in Firstrade value-target planning after safe-haven cash substitution. Unbuyable positive target values are projected to cash before sell and buy planning.

Validation:

• python -m pytest tests/test_execution_service.py -q -k 'projects_unbuyable_value_target_to_zero or leaves_small_safe_haven_target_as_cash or sells_before_buys'
• python -m py_compile application/execution_service.py

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Propagate whole-share-adjusted targets to caller-visible plan

Apply the whole-share compatibility layer before execution result reporting, not only inside execute_value_target_plan: these lines mutate plan locally for order generation, but run_strategy_cycle still reports allocation from the original pre-execution plan (application/rebalance_service.py uses its outer plan at result assembly). When a positive target is projected to zero here, submitted orders follow the adjusted targets while API/notification output still shows the old nonzero target, creating inconsistent and misleading cycle results.

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