feat(ui): maintainer-facing AMS miner contributor-mix dashboard panel

[JSONbored]

Context

#6210 decided the design (see its pinned decision comment): a maintainer-only dashboard panel showing what fraction of a repo's activity comes from identifiable AMS miners and how they perform, keyed on the same GitHub-login identity #6208 already established. This issue is the implementation.

Requirements

• New panel/section in apps/loopover-ui/src/components/site/app-panels/maintainer-panel.tsx (extend the existing panel rather than adding a new route, per this repo's stated dashboard-chrome-reuse preference).
• Backing query: for a repo, classify each submitter login as "has AMS track-record data" (via Implement upgrade-only ORB/AMS reputation bridge (pull, GitHub-login-keyed) #6485's lookup path) vs. not, then compute acceptance rate / review-cycle count / time-to-merge / PR volume per cohort, reusing submitter-reputation.ts's existing review_targets-based outcome classification rather than re-deriving it.
• Bearer-gated, maintainer-only visibility — matches submitter-reputation.ts's own /stats access model. Never a public comment, label, or check-run surface.
• No wallet/hotkey/reward/trust-score wording anywhere in the panel, matching this repo's existing constraints even for private-only surfaces.
• Loading/empty states for a repo with zero identifiable AMS activity (not an error state).

Deliverables

• A new aggregate query (likely in src/db/repositories.ts, alongside where submitter-reputation.ts's outcome data is already read).
• The dashboard panel/section rendering the AMS-vs-human cohort comparison.
• Tests for the aggregate query's cohort classification and metric computation; UI tests for the loading/empty/populated states.

Test Coverage Requirements

The aggregate query lives under src/** and inherits the normal 99%+ Codecov patch requirement. The apps/loopover-ui/** panel itself is outside coverage.include per this repo's convention.

Expected Outcome

A maintainer running ORB can see, on their existing dashboard, what fraction of their repo's contribution activity comes from identifiable AMS miners and how that cohort performs relative to other contributors.

Links & Resources

• Spec: maintainer-facing "AMS miner contributor mix" analytics view #6210 (design decision — read its pinned comment before starting)
• Epic: AMS + ORB combined-use synergy features (both installed on the same repo) #6206 (parent epic)
• Implement upgrade-only ORB/AMS reputation bridge (pull, GitHub-login-keyed) #6485 (the reputation-bridge lookup this reuses for AMS-miner identification)
• apps/loopover-ui/src/components/site/app-panels/maintainer-panel.tsx
• src/review/submitter-reputation.ts (existing per-submitter outcome classification to reuse)

[linear-code]

JSO-4452