Split PriceGatherer and StrategyEvaluator into message-driven workers

[carndog]

Outcome

Run price collection and strategy evaluation as independently testable message-driven workers while preserving the exact monitoring-rule revision used for every decision.

Acceptance criteria

• PriceGatherer publishes PriceObservedV1 after a successful observation write
• StrategyEvaluator resolves the monitoring-rule revision effective at the observation's UTC timestamp
• StrategyEvaluator does not silently substitute a newer current revision when processing a delayed message
• StrategyEvaluator publishes TradeSignalV1 only when warranted
• TradeSignalV1 references the exact immutable monitoring-rule revision used
• Both consumers are idempotent for duplicate delivery
• Correlation and causation identifiers are preserved
• Poison messages are dead-lettered with actionable diagnostics
• End-to-end tests cover delayed processing across a rule activation, retry and duplicate delivery
• Shared domain logic remains independent of Azure Functions and Service Bus
• No RiskGate or broker call is bypassed