V1 Integration (#11183)

Co-authored-by: openhands <openhands@all-hands.dev>
Co-authored-by: sp.wack <83104063+amanape@users.noreply.github.com>
Co-authored-by: Engel Nyst <enyst@users.noreply.github.com>

openhands/app_server/event_callback/README.md

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+# Event Callbacks
+
+Manages webhooks and event callbacks for external system integration.
+
+## Overview
+
+This module provides webhook and callback functionality, allowing external systems to receive notifications when specific events occur within OpenHands conversations.
+
+## Key Components
+
+- **EventCallbackService**: Abstract service for callback CRUD operations
+- **SqlEventCallbackService**: SQL-based callback storage implementation
+- **EventWebhookRouter**: FastAPI router for webhook endpoints
+
+## Features
+
+- Webhook registration and management
+- Event filtering by type and conversation
+- Callback result tracking and status monitoring
+- Retry logic for failed webhook deliveries
+- Secure webhook authentication