feat(mcp): per-server tool filtering via include/exclude and enabled flag

[teyrebaz33]

Problem

When an MCP server exposes many tools, there is no way to restrict which ones Hermes registers. This causes tool list bloat and can expose dangerous tools (e.g. delete_customer) that the user never intends to use.

Solution

Add optional config keys under each mcp_servers entry:

mcp_servers:
  github:
    url: https://mcp.github.com
    tools:
      include: [create_issue, list_issues]   # whitelist — only these are registered
  stripe:
    url: https://mcp.stripe.com
    tools:
      exclude: [delete_customer]             # blacklist — all except these
  legacy:
    url: https://mcp.legacy.internal
    enabled: false                           # skip server entirely (no connection attempt)

Rules

• include takes precedence over exclude if both are set
• Neither key → all tools registered (fully backward-compatible)
• enabled: false short-circuits before any network call

Changes

• tools/mcp_tool.py: filter loop in _discover_and_register_server, enabled check in discover_mcp_tools
• tests/tools/test_mcp_tool.py: TestMCPSelectiveToolLoading — 4 tests (include, exclude, no-filter, enabled=false)

Test results

134 passed, 1 warning in 9.74s