feat(alerts): add Alert Manager for orchestration and routing - Issue #38 (55 tests)

Implements comprehensive alert management framework:
- AlertPriority, AlertCategory, AlertStatus, ChannelType enums
- AlertTemplate, RateLimitConfig, RoutingRule dataclasses
- Alert, DeliveryResult, AlertStats tracking classes
- LogChannel and WebhookChannel implementations
- AlertManager main class

Features:
- Multi-channel alert routing (log, webhook, slack, sms, email, push)
- Configurable routing rules based on priority and category
- Rate limiting to prevent alert storms
- Duplicate detection and suppression
- Alert history with filtering and search
- Alert acknowledgement tracking
- Template-based alert formatting
- Synchronous and asynchronous delivery
- Statistics and metrics tracking
- Convenience methods for trade/risk/execution alerts

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>