Research skill manifest format (research_skills/<name>/SKILL.md)

Idea adapted from the SKILL.md layout used by HKUDS/Vibe-Trading and spyderweb47/Vibe-Trade (idea only, no code). Each research skill gets a folder with a SKILL.md whose YAML-style front matter must contain: name, callable, category: research, research_only: true, inputs, output, lookahead, data_status, wired_into_execution: false, attribution. tests/test_research_extracts.py checks every manifest: the callable exists in crew.skills.REGISTRY, is flagged research-only, and its name does not appear in engine/risk/order code. Manifests are documentation and metadata; nothing loads or executes code from them.