- Add APP_CREATED, APP_UPDATED, APP_DELETED counters to EnterpriseTelemetryCounter
- Create EnterpriseTelemetryEvent StrEnum for type-safe event names
- Update metric_handler to use new app-specific counters with labels (tenant_id, app_id, mode)
- Convert all event_name strings to EnterpriseTelemetryEvent enum values
- Update exporter to create OTEL meters for new app counters (dify.app.created.total, etc.)
- Update tests to verify new counter behavior and enum usage