feat(alerting): server-side state+severity filters, ButtonGroup filter UI

Backend: `GET /environments/{envSlug}/alerts` now accepts optional multi-value
`state=…` and `severity=…` query params. Filters are pushed down to
PostgresAlertInstanceRepository, which appends `AND state::text = ANY(?)` /
`AND severity::text = ANY(?)` to the inbox query (null/empty = no filter).

`AlertInstanceRepository.listForInbox` gained a 7-arg overload; the old 5-arg
form is preserved as a default delegate so existing callers (evaluator,
AlertingFullLifecycleIT, PostgresAlertInstanceRepositoryIT) compile unchanged.
`InAppInboxQuery.listInbox` also has a new filtered overload.

UI: InboxPage severity filter migrated from `SegmentedTabs` (single-select,
no color cues) to `ButtonGroup` (multi-select with severity-coloured dots),
matching the topnavbar status-filter pattern. `useAlerts` forwards the
filters as query params and cache-keys on the filter tuple so each combo
is independently cached.

Unit + hook tests updated to the new contract (5 UI tests + 8 Java unit
tests passing). OpenAPI types regenerated from the fresh local backend.

ui/src/pages/Alerts/InboxPage.tsx

@@ -2,9 +2,9 @@ import { useMemo, useState } from 'react';
 import { Link } from 'react-router';
 import { Inbox } from 'lucide-react';
 import {
-  Button, DataTable, EmptyState, SegmentedTabs, useToast,
+  Button, ButtonGroup, DataTable, EmptyState, useToast,
 } from '@cameleer/design-system';
-import type { Column } from '@cameleer/design-system';
+import type { ButtonGroupItem, Column } from '@cameleer/design-system';
 import { PageLoader } from '../../components/PageLoader';
 import { SeverityBadge } from '../../components/SeverityBadge';
 import { AlertStateChip } from '../../components/AlertStateChip';
@@ -20,20 +20,21 @@ import tableStyles from '../../styles/table-section.module.css';
 
 type Severity = NonNullable<AlertDto['severity']>;
 
-const SEVERITY_FILTERS: Record<string, { label: string; values: Severity[] | undefined }> = {
-  all:      { label: 'All severities', values: undefined },
-  critical: { label: 'Critical',       values: ['CRITICAL'] },
-  warning:  { label: 'Warning',        values: ['WARNING'] },
-  info:     { label: 'Info',           values: ['INFO'] },
-};
+const SEVERITY_ITEMS: ButtonGroupItem[] = [
+  { value: 'CRITICAL', label: 'Critical', color: 'var(--error)' },
+  { value: 'WARNING',  label: 'Warning',  color: 'var(--warning)' },
+  { value: 'INFO',     label: 'Info',     color: 'var(--text-muted)' },
+];
 
 export default function InboxPage() {
-  const [severityKey, setSeverityKey] = useState<string>('all');
-  const severityFilter = SEVERITY_FILTERS[severityKey];
+  const [severitySel, setSeveritySel] = useState<Set<string>>(new Set());
+  const severityValues: Severity[] | undefined = severitySel.size === 0
+    ? undefined
+    : [...severitySel] as Severity[];
 
   const { data, isLoading, error } = useAlerts({
     state: ['FIRING', 'ACKNOWLEDGED'],
-    severity: severityFilter.values,
+    severity: severityValues,
     limit: 200,
   });
   const bulkRead = useBulkReadAlerts();
@@ -179,10 +180,10 @@ export default function InboxPage() {
           <span className={css.pageSubtitle}>{subtitle}</span>
         </div>
         <div className={css.pageActions}>
-          <SegmentedTabs
-            tabs={Object.entries(SEVERITY_FILTERS).map(([value, f]) => ({ value, label: f.label }))}
-            active={severityKey}
-            onChange={setSeverityKey}
+          <ButtonGroup
+            items={SEVERITY_ITEMS}
+            value={severitySel}
+            onChange={setSeveritySel}
           />
         </div>
       </header>