Epic: rule-based eligibility for scoring labels — enforce label policy in the pipeline, not by judgment

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Problem

Scoring labels are economic parameters: on gittensor-scored repos, the label a merged contribution carries sets its payout multiplier, with gittensor:priority at the top of the range. Today the constraint on how those labels are applied is maintainer policy — a stated practice, not a mechanical rule. Anything that moves payout should be enforced by the trusted label pipeline itself, so the policy is auditable, uniform across every repo ORB manages, and impossible to deviate from unintentionally.

Goal

Label policy becomes code: eligibility rules evaluated by the pipeline on every labeling event, with automatic correction, a visible audit trail, and published documentation. No labeling decision that affects scoring rests on memory or discretion.

Sub-issues

• author-based eligibility rule: gittensor:priority valid only on maintainer-authored issues, auto-stripped elsewhere
• open-window rule: priority issues must be publicly visible for a minimum window before PRs against them are gate-eligible

Acceptance

Both rules active in the trusted label pipeline across all managed repos, each enforcement action logged to the decision ledger, and the policy documented on the public docs site. A policy deviation is structurally impossible rather than merely against stated practice.

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JSO-6799