Add per-agent MCP tool filtering

[mingshl]

Originally created by @mingshl in mingshl/opensearch-agent-server#17

Description

Currently all agents get all MCP tools. Different agents should have different tool sets based on their specialization.

Design

• The fallback agent should have access to all OpenSearch MCP tools
• The ART agent should only have search-relevance tools
• Tool profiles should be configurable per agent via YAML or config

Acceptance Criteria

• Each agent type can specify which MCP tools it needs
• Tool filtering applied at agent creation time
• Configuration-driven (not hardcoded)
• Fallback agent retains all tools

References

• Agent factories: src/agents/