docs: add AgentScope MCP integration guide

[wayyoungboy]

Summary

Closes #111.

• Add an AgentScope integration guide that connects PowerMem through powermem-mcp streamable HTTP.
• Show how to register PowerMem MCP tools into an AgentScope Toolkit.
• Add function-level search_memories usage and verification/troubleshooting notes.
• Link the guide from the README integration table and integrations overview.

Validation

• git diff --cached --check
• pnpm run build from docs/website

[lightzt99]

I tested the code examples in this guide against AgentScope 2.0.1 (latest on PyPI) and found the documented API does not match the actual package:

API mismatches between the guide and agentscope 2.0.1:

Guide (this PR)	AgentScope 2.0.1 actual
HttpStatelessClient(name=..., transport="streamable_http", url=...)	MCPClient(name=..., is_stateful=False, mcp_config=HttpMCPConfig(url=...))
toolkit.register_mcp_client(client, group_name=...)	Toolkit has no MCP-related methods
toolkit.get_json_schemas()	toolkit.get_tool_schemas()
client.get_callable_function(func_name=..., wrap_tool_result=...)	await client.get_tool(name) (returns MCPTool)

What does work: MCPClient.connect() → list_tools() → get_tool() → call the tool — the integration approach is valid, the PowerMem MCP server side is fine, and the AgentScope MCP client can talk to it.

The code snippets in the guide need to be rewritten to match the actual agentscope 2.x API. The agentscope.io MCP tutorial still shows the older API used in this guide, so this may be a version mismatch on their side, but the guide should match what users get from pip install agentscope today.

[wayyoungboy]

Updated the AgentScope guide to match the current MCP client API: it now uses MCPClient with HttpMCPConfig, lists tools through list_tools(), and calls individual tools through get_tool(). I also removed the outdated Toolkit registration wording from the README and integration overview.

[lightzt99]

LGTM