feat(web): silence alerts from the hub, a rule or an incident - #2292

🟢 Confidence 9/10 · safe to merge. Only the four earlier info-level defects remain open; the group label at incident/update.ts:104 is the one that misstates a silence's scope.
_{4 notes · tests covered · risk medium · 0/1 new units observable −1}

Adds a Silences tab to the alerts hub plus a Silence action, badge and shared dialog on the rule and incident pages. The client mirrors the server's matching rules; four earlier info-level defects are still present and no new defects were found.

• listSilences/activeSilenceFor in shared/silences.ts read active, scheduled and ended silences and re-derive status from the window
• SilenceDialog submodel computes 1h/4h/next-09:00/custom ends and saves through createSilence
• Hub Silences tab lists and ends silences, gated on alerts:manage
• Rule and incident headers show a silence badge and a Silence action scoped to the incident's group

Still open from earlier reviews

• 🔵 Note · F10 · A silence on an incident without a rule row never shows the badge · apps/web/src/page/alerts/incident/view.ts:155
• 🔵 Note · F11 · The rule page's group-named badge branch has no test · apps/web/src/page/alerts/rule/view.ts:112
• 🔵 Note · F8 · A silence on a deleted rule reads rule deleted rule · apps/web/src/page/alerts/hub/view-silences.ts:151
• 🔵 Note · F9 · Group label names a scope matchersForRule did not apply · apps/web/src/page/alerts/incident/update.ts:104

Fixed since the last review

• ✅ F7 · A morning silence saved after 09:00 lands a day later than the label says

_{dc49d67 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}