Show which cluster an incident came from, as a chip

A team with one Alertmanager per Kubernetes cluster could not tell at a
glance where an incident started: the cluster was only a word inside the
title. When an alert carries a `cluster` label, the queue rows, the incident
page and the alerts list now show it as a chip in that cluster's colour, a
stable pick from the existing six-colour palette. A queue row drops
`cluster=...` from its title, since the chip says it, and the incident page
keeps the full title.

An incident has the label only when it is in Alertmanager's group_by, which
is also what keeps two clusters' identical alerts apart: incidents are matched
on the team and the groupKey, and the groupKey does not include external
labels. The README has a section on the two settings (Prometheus
externalLabels and group_by). The alerts list reads the label from the alert
itself, so it shows the chip with only the external label.

Web UI and docs only: no endpoint or JSON shape changed, so nothing to mirror
in terdut-tui. Nothing changes for a team whose alerts have no cluster label.

internal/web/static/js/queue.js

@@ -1,8 +1,8 @@
 // The incident queue: filter chips and a list of incident rows.
 
 import * as api from './api.js';
-import { h, clear, badge, severityBadge, emptyState, spinner, fadeOnOverflow } from './ui.js';
-import { ago, until, isFuture, severityClass, labelSummary } from './format.js';
+import { h, clear, badge, severityBadge, originChip, emptyState, spinner, fadeOnOverflow } from './ui.js';
+import { ago, until, isFuture, severityClass, labelSummary, originOf, titleWithoutOrigin } from './format.js';
 import { state, myID, onTeamChange } from './state.js';
 import * as onboarding from './onboarding.js';
 import { navigate } from './app.js';
@@ -201,15 +201,18 @@ function row(inc, index) {
     ? h('span', { class: 'row-team', text: inc.team_name })
     : null;
 
+  const origin = originOf(inc.group_labels);
+
   return h('a', {
     class: `row ${severityClass(inc.severity)} ${resolved ? 'resolved' : ''} ${index === cursor ? 'kbd-focus' : ''}`,
     href: `/incidents/${inc.id}`,
     'aria-current': inc.id === selected ? 'true' : null,
     dataset: { index: String(index) },
   },
-    h('div', { class: 'row-title', text: inc.title }),
+    h('div', { class: 'row-title', text: titleWithoutOrigin(inc.title, origin) }),
     h('div', { class: 'row-age', title: inc.triggered_at, text: `Triggered ${ago(inc.triggered_at)}` }),
     h('div', { class: 'row-meta' },
+      origin && originChip(origin),
       !impliedStatus && status,
       // The left-border colour alone doesn't say what it means; spell it out
       // too, same badge the incident detail page uses for severity.