fix(web-ui): display all human-facing timestamps in Asia/Jerusalem (deterministic)

Storage stays UTC (DB TIMESTAMPTZ, API ISO-UTC) — only the display layer is
localized, and now deterministically: every timestamp renders pinned to
Asia/Jerusalem via a single Intl-based formatter, so SSR (UTC container) and
the browser agree on any runtime. No layout/visible-format change — only the tz.

- New single date formatter web-ui/src/lib/format-date.ts (G2): formatDate /
  formatDateShort / formatDateLong / formatDateTime / formatDateTimeFull /
  formatTime / formatIsoDate + Israel helpers getIsraelYear / israelDayKey /
  israelMidnightMs / israelParts + formatRelative (long/short/tight wording).
- Routed all ad-hoc toLocaleDateString/toLocaleTimeString/toLocaleString +
  hand-rolled new Date(...).get*() / toISOString().slice(0,10) timestamp call
  sites (30 files) through it. Number toLocaleString left untouched.
- Spec: added INV-UI9 to docs/spec/X6 (UTC storage, Asia/Jerusalem display).

Display-only; no layout/design/IA change → Claude Design gate N/A.
Invariants: G2 (single date formatter, no parallel ad-hoc formatting), INV-UI9.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-ui/src/components/cases/agent-activity-preview.tsx

@@ -4,6 +4,7 @@ import Link from "next/link";
 import { Loader2, CheckCircle2, Clock } from "lucide-react";
 import { useAgentActivity } from "@/lib/api/agents";
 import type { PaperclipIssue } from "@/lib/api/agents";
+import { formatRelative } from "@/lib/format-date";
 
 const STATUS_DOT: Record<string, string> = {
   in_progress: "bg-gold",
@@ -22,13 +23,7 @@ const STATUS_LABEL: Record<string, string> = {
 };
 
 function timeAgo(iso: string | null): string {
-  if (!iso) return "—";
-  const diffMs = Date.now() - new Date(iso).getTime();
-  const m = Math.floor(diffMs / 60_000);
-  if (m < 60) return `לפני ${m}ד'`;
-  const h = Math.floor(m / 60);
-  if (h < 24) return `לפני ${h}ש'`;
-  return `לפני ${Math.floor(h / 24)} ימים`;
+  return formatRelative(iso, { units: "tight", fallback: "—" });
 }
 
 function IssueRow({ issue }: { issue: PaperclipIssue }) {