feat(coming-soon): premium themed redesign with launch countdown

Full refactor of the maintenance/coming-soon page for all locales (de/en/ar,
RTL-aware) with a refined, theme-aware (light + dark) premium composition:
glass panel, live status indicator, hero title, description, launch countdown
and CTAs. Reuses the existing hero/motion system; no new dependencies.

- Add components/site/launch-countdown.tsx: hydration-safe client countdown
  (days/hours/minutes/seconds), localized labels, Arabic-aware typography,
  "launched" fallback when the target passes.
- Rewrite app/[locale]/coming-soon/page.tsx around the countdown and a single
  easy-to-edit LAUNCH_DATE_ISO constant (default ~45 days out).
- Add comingSoon i18n keys (status, countdownLabel, unit labels, launched)
  to en/de/ar.

messages/de.json

@@ -28,7 +28,14 @@
     "titleLineThree": "bald wieder online",
     "description": "Ich baue die Website neu auf, damit Leistungen, ausgewählte Arbeiten und Zusammenarbeit klarer, direkter und ohne Wiederholungen sichtbar werden.",
     "primaryCta": "Projekt starten",
-    "secondaryCta": "Zur Startseite"
+    "secondaryCta": "Zur Startseite",
+    "status": "In Entwicklung · bald zurück",
+    "countdownLabel": "Start in",
+    "unitDays": "Tage",
+    "unitHours": "Stunden",
+    "unitMinutes": "Minuten",
+    "unitSeconds": "Sekunden",
+    "launched": "Wir starten sehr bald"
   },
   "homepage": {
     "meta": {