feat(scoring): detect approved and mergeable pending PR scenarios

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Problem

Miners often need to understand near-term scoreability when approved PRs are expected to merge or close. Today scenario previews depend too much on manually supplied assumptions.

Desired behavior

Detect a contributor’s open PR state across registered repos, identify approved/mergeable/stale/draft/blocked PRs, and feed realistic pending-work scenarios into private score previews.

Implementation notes

• Use cached GitHub PR, review, check, and mergeability data where available.
• Keep official Gittensor data authoritative for recognized history.
• Add scenario fields such as current, after approved PRs merge, after stale PRs close, and best reasonable case.
• Label every projection as an estimate or observed scenario. Never imply guaranteed outcomes.

Public/private boundaries

Scenario score previews are private API/MCP only. Public GitHub comments must not include score estimates, payout language, wallets, hotkeys, or raw trust signals.

Acceptance criteria

• Approved but unmerged PRs affect projected open PR pressure.
• Draft/stale/blocked PRs are not treated as likely-to-land.
• Maintainer-authored PRs on maintained repos are handled as maintainer-lane context.
• Current effective score and underlying potential remain distinct.
• User-supplied assumptions are labeled separately from GitHub-observed state.

Tests

• Approved-but-unmerged PR scenario.
• Closed PR scenario.
• Draft PR scenario.
• Stale PR scenario.
• Maintainer-authored PR scenario.
• Public sanitizer regression for score/reward/wallet/hotkey language.