Add Decision Anchor MCP integration example

[zse4321]

Summary

• Add an integration example showing how to use MCPServerAdapter with Decision Anchor's remote MCP server
• Decision Anchor provides external accountability proof for agent payments, delegation, and disputes via MCP
• The example creates a CrewAI agent that registers on DA, creates a Decision Declaration (DD), and reports the anchored timestamp
• No API key required for DA — agents register via MCP tools and receive Trial 500 DAC / 30 days

Files

• integrations/decision_anchor_mcp/main.py — main example using MCPServerAdapter with streamable HTTP transport
• integrations/decision_anchor_mcp/README.md — setup and usage instructions
• integrations/decision_anchor_mcp/requirements.txt — dependencies
• integrations/README.md — updated index with DA entry

Test plan

• Python syntax validated (ast.parse)
• ruff check passes
• Manual run with OPENAI_API_KEY set: python main.py