feat: add health check endpoint and notification provider abstraction

[akordavid373]

• Implements issue Add Health Check Endpoint #84: Add Health Check Endpoint

  • GET /api/health returns full dependency status (database)
  • GET /api/health/live returns lightweight liveness probe
  • HealthService checks PostgreSQL via TypeORM DataSource
  • Extensible: adding a new dependency check is a single method

• Implements issue Create Notification Provider Abstraction #74: Create Notification Provider Abstraction

  • INotificationProvider interface (sendAlert, isHealthy, providerName)
  • NotificationPayload type shared across all providers
  • DiscordNotificationProvider conforms to the interface
  • TelegramNotificationProvider conforms to the interface
  • NotificationsService dispatches to all registered providers
  • New providers added via factory in NotificationsModule

Closes #84, Closes #74

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Related Issues

Fixes #
Related to #

Changes Made

Testing

• I have tested these changes locally
• Tests pass locally (npm run test)
• Linting passes (npm run lint)
• Code is formatted (npm run format)
• TypeScript builds successfully (npm run build)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests passed with my changes

Screenshots (if applicable)

Additional Context