feat(analytics): add role activation and retention rollups

[JSONbored]

Parent phase: #237
Parent roadmap: #127

Problem

Operators need to know whether miners, maintainers, repo owners, and contributors are actually activating and returning across the product surfaces.

Acceptance criteria

• Rollups compute activation and retention by role, surface, and coarse time window.
• Metrics separate CI/check state, reviewer/mergeability state, and adoption/usage state where relevant.
• Rollups do not expose individual private activity where aggregate reporting is enough.

Validation expected

• Rollup tests cover empty, single-role, multi-role, and stale-data cases.
• API tests verify aggregate shape and privacy boundaries.

Public-output safety criteria

• Public text is sanitized before reaching GitHub comments, issue bodies, PR bodies, extension-visible public panels, or copied public snippets.
• Tests cover forbidden wallet/hotkey, reward-estimate, trust-score, public-score-prediction, private-reviewability, private-scoreability, and farming-language leakage.

Cross-cutting acceptance criteria

• Preserve the repo quality gate: npm run test:ci, 97%+ global coverage, and the local branch coverage target for touched code.
• Keep public/private boundaries explicit. Public GitHub output must not expose wallets, hotkeys, reward estimates, raw trust scores, public score predictions, private reviewability, private scoreability context, or farming language.
• Add/update focused tests for the changed behavior instead of relying on green checks alone.