Record the decisions a Bot considered and rejected (#396) #565

What

Part of #396 (child of #386). A Bot often considers a correct or risky option, then decides not to use it; those "considered and rejected" choices are invisible today, so a reviewer cannot see near-misses or judgment drift.

Expected behavior

• A Bot tool record_decision({ option, choice, why }) (choice: used | rejected) writes one JSON line to <home>/decisions.jsonl — capped (2000 lines), append-only, written by the host so a Bot cannot edit or delete a past entry — and fires the entry on the activity feed as decision.
• Opt-in: with config.decisions off (default) the tool is not registered, nothing is written and no event is fired.
• A key, token or password in the text is refused, so the log needs no secret.

Change scope

New core/src/host/decisions.js; core/src/host/hooks.js (rt.fireFeed); core/src/host/flybot-feed.js + core/types/flybot.d.ts (the decision feed event); core/index.js (module order); test core/test/decisions.test.js; docs/subsystems/{core-host,plugin-runtime}.md. No new dependency; local only; default off.

Why

An auditable log of agent decisions is the safety/audit direction (#386/#396) and is industrial (compliance, post-hoc review) without a parallel system.