Replaces the confusing mix of enabled_tools + mcp_servers + subagent_tools
with a single explicit structure:

    tools: {
      agent:   {native: [...], mcp: {server: [groups]}},
      subagent:{native: [...], mcp: {server: [groups]}}
    }

Why:
- Old fields mixed native and MCP names (mcp__server__tool) in one list,
  making it impossible to tell at a glance what a subagent actually gets.
- subagent_runner.py had 25 lines of runtime MCP filtering logic that
  was hard to follow and error-prone.

Changes:
- AgentProfile: add ToolConfig / ToolScopeConfig pydantic models,
  keep old fields (enabled_tools, mcp_servers, subagent_tools) for
  auto-migration via _migrate_tools validator.
- loader.py: read new "tools" key, auto-migrate legacy configs.
- agent.py: _tool_list now accepts ToolScopeConfig.
- subagent_runner.py: simplified — profile.get_subagent_tools() returns
  the exact scope, no runtime filtering needed.
- context_builder.py, list_tools.py, spawn_agent.py: updated to use
  profile.get_agent_tools() / get_subagent_tools().
- All 6 profile config.json files migrated to new schema.
- Secretary subagent now explicitly gets navi-web MCP tools for web search.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>