feat: Add alert endpoints to alert_processor service for dashboard

Implemented missing alert endpoints that the dashboard requires for
health status and action queue functionality.

Alert Processor Service Changes:
- Created alerts_repository.py:
  * get_alerts() - Filter alerts by severity/status/resolved with pagination
  * get_alerts_summary() - Count alerts by severity and status
  * get_alert_by_id() - Get specific alert

- Created alerts.py API endpoints:
  * GET /api/v1/tenants/{tenant_id}/alerts/summary - Alert counts
  * GET /api/v1/tenants/{tenant_id}/alerts - Filtered alert list
  * GET /api/v1/tenants/{tenant_id}/alerts/{alert_id} - Single alert

- Severity mapping: "critical" (dashboard) maps to "urgent" (alert_processor)
- Status enum: active, resolved, acknowledged, ignored
- Severity enum: low, medium, high, urgent

API Server Changes:
- Registered alerts_router in api_server.py
- Exported alerts_router in __init__.py

Procurement Client Changes:
- Updated get_critical_alerts() to use /alerts path
- Updated get_alerts_summary() to use /alerts/summary path
- Added severity mapping (critical → urgent)
- Added documentation about gateway routing

This fixes the 404 errors for alert endpoints in the dashboard.

services/alert_processor/app/api/__init__.py

@@ -3,5 +3,6 @@ Alert Processor API Endpoints
 """
 
 from .analytics import router as analytics_router
+from .alerts import router as alerts_router
 
-__all__ = ['analytics_router']
+__all__ = ['analytics_router', 'alerts_router']