feat(signals): add bounty and opportunity stale-source reconciliation

[JSONbored]

Parent roadmap: #82

Background

Bounty/opportunity context can become stale, completed, cancelled, or ambiguous. Miners should not be guided toward dead work.

Goal

Reconcile bounty and opportunity sources with issue/PR state and feed stale-state warnings into opportunity ranking.

Current Behavior

Bounty lifecycle work exists as a direction, but source freshness and stale-opportunity reconciliation need stronger modeling.

Desired Behavior

MCP/API guidance distinguishes active, stale, completed, cancelled, ambiguous, and linked-PR bounty/opportunity states.

Implementation Requirements

• Ingest or refresh bounty/opportunity source metadata.
• Link issues and PRs where discoverable.
• Mark stale/completed/cancelled/ambiguous states.
• Feed state into issue quality and next-work ranking.
• Avoid public score/reward language.

Public/Private Output Boundaries

Signal data can inform private API/MCP outputs. Public GitHub output must use only sanitized, maintainer-friendly summaries and must not expose private scoreability or contributor scoring internals.

Acceptance Criteria

• Active context is distinguished from historical context.
• Dead opportunities are not recommended as top work.
• Ambiguous state produces caution.
• Linked PR state is included when available.

Testing Requirements

• npm run test:ci must pass.
• Global coverage must remain at or above 97% for lines, statements, functions, and branches.
• Aim for 98%+ branch coverage locally to avoid CI variance.
• Add tests for every new branch, fallback path, sanitizer rule, and regression.
• Add invariant/property-style tests when behavior depends on sorting, gating, scoring, queue pressure, source-upload safety, public/private boundaries, or upstream drift.
• Public GitHub output must be tested against forbidden language: wallet, hotkey, raw trust score, payout, reward estimate, farming, private reviewability, and public score estimate.
• MCP/local tooling must prove source contents are not uploaded.

Additional Test Scenarios

• Active fixture.
• Completed fixture.
• Cancelled fixture.
• Stale fixture.
• Linked PR fixture.
• Public wording regression.