refactor: share LongBridge paper command lifecycle

[Pigbibi]

Summary

• retain LongBridge-specific position and quote reconciliation only
• move durable command claim, release/admission checks, runtime gate receipts, and state transitions to QuantPlatformKit
• preserve the isolated paper-only endpoint and its default-disabled runtime guard
• assert the nested, redacted platform proposal payload emitted by the shared contract

Verification

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 PYTHONPATH=/tmp/qsl-qpk-paper-command-core/src:. python -m pytest -q tests/test_paper_execution_command_consumer.py
• PYTHONPATH=/tmp/qsl-qpk-paper-command-core/src:. python -m compileall -q application/paper_execution_command_consumer.py tests/test_paper_execution_command_consumer.py
• git diff --check

The local HTTP-layer tests require numpy, which is not installed on this constrained VPS; repository CI installs the declared dependencies. No deployment, scheduler, broker adapter, or live execution path changes.