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/training/lessons-tab.tsx

@@ -37,6 +37,7 @@ import {
   usePatchLesson,
   type DecisionLesson,
 } from "@/lib/api/training";
+import { formatDateShort } from "@/lib/format-date";
 
 const CATEGORIES = [
   { value: "general", label: "כללי" },
@@ -224,7 +225,7 @@ function LessonItem({
             {reviewBadge.label}
           </Badge>
           <span className="grow text-ink-muted tabular-nums">
-            {new Date(lesson.created_at).toLocaleDateString("he-IL")}
+            {formatDateShort(lesson.created_at)}
           </span>
         </div>