feat(agent): add repo-specific scenario simulator

[JSONbored]

Parent roadmap: #127
Parent phase: #269

Goal

Add a repo-specific scenario simulator so miners can compare open, merge, close, wait, and cleanup-first choices before creating more work.

This issue is now a mini-epic. Do not implement the full simulator in one PR; use the focused child issues below.

Child issues

• feat(agent): add scenario input model and assumptions #286 add scenario input model and assumptions
• feat(scoring): simulate open-pr pressure scenarios #287 simulate open-pr pressure scenarios
• feat(scoring): simulate linked-issue and branch eligibility scenarios #288 simulate linked-issue and branch eligibility scenarios
• feat(signals): include duplicate and stale-work scenario blockers #289 include duplicate and stale-work scenario blockers
• feat(agent): render public-safe scenario summaries #290 render public-safe scenario summaries

Done when

• Scenario inputs, open-PR pressure, linked-issue/branch eligibility, duplicate/stale blockers, and public-safe summaries are complete or intentionally superseded.
• Scenario output distinguishes facts, assumptions, estimates, and missing data.
• Public-safe summaries omit private scoreability, reward/risk, wallet, hotkey, and trust context.

Non-goals

• No public reward prediction or payout claims.
• No autonomous PR bot.
• No public raw trust score, private reviewability, or private scoreability output.

Validation expected

• Child PRs should include targeted scenario fixtures, sanitizer coverage, and npm run test:ci.