feat(overview): give analysts an Overview that says whether the product is working - #2555

🟢 Confidence 10/10 · safe to merge. Verdict derivation is unit-pinned and every read state (clear, attention, empty, loading, failed+retry) has a scene test; only the tail of the new scene test went unread.
_{no findings · tests covered · risk medium}

An analyst now gets a verdict page on Overview: one sentence with the counts behind it, four linked panels and a failure slot per read, gated on the audience the shell already reads. Web-only and contained; safe to merge.

• verdictOf derives clear, attention, empty, loading and per-read-failed states from three slots
• initWith/revive require context.audience; a late-arriving role mounts and starts the reads
• pageTitle gains wrap, and the SLO burning rule moves to alerts/shared/slo-derive.ts
• Alerts hub and investigation detail drop their write controls for an analyst

_{a3f0e44 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}