Update Workflows Integration documentation for PR #799

Comprehensive update to Workflows integration documentation based on changes
from cloudflare/agents PR #799: feat: Add Cloudflare Workflows integration for Agents.

Changes:
- Replace basic workflow triggering guide with comprehensive integration documentation
- Add AgentWorkflow base class reference with typed Agent access
- Document lifecycle callbacks (onWorkflowProgress, onWorkflowComplete, onWorkflowError, onWorkflowEvent)
- Add workflow tracking system documentation (cf_agents_workflows table, metadata querying)
- Document Agent workflow methods (runWorkflow, sendWorkflowEvent, getWorkflow, getWorkflows, deleteWorkflow, deleteWorkflows)
- Add approval methods (approveWorkflow, rejectWorkflow, waitForApproval)
- Include patterns for background processing, human-in-the-loop approvals, retry logic, and state synchronization
- Add bidirectional communication examples (Workflow to Agent and Agent to Workflow)
- Document best practices including workflow cleanup strategies

This update provides developers with a complete reference for integrating
Cloudflare Workflows with Agents for durable, multi-step background processing.

Source PR: cloudflare/agents#799

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: github-actions[bot]