refactor(agent): extract nested science experts

[JaimeCernuda]

Summary

• extract executable NDPExpert and SACFormatExpert child expert classes
• register the nested experts as real dispatch targets instead of compatibility aliases through Data/Analysis
• keep Data/Analysis as top-level managers that delegate NDP/SAC work through child experts
• update tests to assert top-level tool lists no longer directly own NDP/SAC tools
• record the completed extraction and remaining shared-model caveat in TASK.md

Verification

• uv run ruff check src/ tests/ scripts/create_demo_data.py
• uv run pytest tests/test_core/test_agent_planner.py::TestBuildCapabilitiesContext tests/test_core/test_agent_planner.py::TestRunAgentLoop::test_ndp_tool_action_is_promoted_to_nested_catalog_expert tests/test_core/test_agent_dispatch.py tests/test_gact/test_agents_catalog.py tests/test_tools/test_ndp_server.py tests/test_tools/test_sac_server.py tests/test_experts/test_analysis_expert.py tests/test_experts/test_data_expert.py -q (106 passed)
• uv run pytest tests/ -q (1152 passed, 37 skipped, 81% coverage)