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/app/skills/page.tsx

@@ -13,6 +13,7 @@ import {
   TableRow,
 } from "@/components/ui/table";
 import { useSkills, type Skill } from "@/lib/api/skills";
+import { formatIsoDate } from "@/lib/format-date";
 
 function formatChars(skill: Skill): string {
   // Mockup column = "גודל (תווים)" — the DB markdown char count, grouped.
@@ -21,13 +22,8 @@ function formatChars(skill: Skill): string {
 }
 
 function formatUpdated(iso: string | null): string {
-  if (!iso) return "—";
-  try {
-    // ISO-style date to match the mockup (2026-06-09), tabular.
-    return new Date(iso).toISOString().slice(0, 10);
-  } catch {
-    return "—";
-  }
+  // ISO-style date to match the mockup (2026-06-09), tabular — Israel-time day.
+  return formatIsoDate(iso);
 }
 
 /**