Unify Decodex research method

[yvette-carlisle]

Summary

• add Decodex-owned bounded research phase skills for probe, evidence, options, judgment, challenge, decision, and promotion
• route plugin/docs away from the legacy external research default and toward runtime-local Decision Contracts
• tighten decision_ready compiler validation so options, challenge notes, and validation expectations are required

Verification

• cargo test -p decodex --lib plugin_surface_tests -- --nocapture
• cargo test -p decodex --lib research_design -- --nocapture
• decodex research compile forward-test: draft_latent, authority=false
• decodex intake goal forward-test before promote: rejected draft_latent
• decodex research promote forward-test: accepted_promoted, authority=true
• decodex intake goal --dry-run forward-test after promote: applied=false, persisted=false
• cargo make check