Show next scheduled sync time on every page

Exposes the scheduler's next_tick in the topbar via a safe Jinja
helper (falls back to nothing if the scheduler isn't running yet),
and converts the server-rendered UTC timestamp to the visitor's local
time client-side so it reads correctly regardless of timezone.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/web/routes.py

@@ -15,6 +15,14 @@ router = APIRouter()
 templates = Jinja2Templates(directory=str(Path(__file__).resolve().parent / "templates"))
 
 
+def _next_sync_tick(request: Request):
+    scheduler = getattr(request.app.state, "scheduler", None)
+    return getattr(scheduler, "next_tick", None)
+
+
+templates.env.globals["next_sync_tick"] = _next_sync_tick
+
+
 def _get_user_or_404(repository: UserRepository, user_id: int) -> SyncUser:
     user = repository.get(user_id)
     if user is None: