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## Task
Implement single-tick update loop

Use one setInterval(1000) that updates the main clock and all five city card clocks simultaneously each second without page reload.

Current phase: Timezone Logic & Clock Engine

Project context: الساعة العالمي — الساعة العالمية في جيبك

## Deliverable quality baseline (applies to user-facing output)
If this task produces or changes anything the user sees in a browser, the result must look deliberately crafted — never scaffold-like or raw default markup:
- Clear visual hierarchy: a real page structure with headings, grouping and whitespace — not a bare dump of unstyled elements.
- Deliberate typography and spacing: readable font sizes and line-height, consistent padding/margins; interactive controls (buttons, inputs, links) must be visibly styled, never browser-default only.
- A coherent, restrained color palette (background, text, accent) with accessible contrast.
- Responsive layout: the page must stay usable on a narrow (mobile) viewport.
- Interactions must genuinely work: every control the description asks for performs the requested behavior, and purely local behavior (e.g. a confirmation/status message on click) is implemented client-side — no external service is needed for simple local feedback.
- Accessibility basics: semantic HTML, labels for inputs, alt text for images.
- Arabic/RTL correctness: the document must set lang="ar" and dir="rtl", declare UTF-8 charset, and use natural Arabic wording and typography (no machine-stiff phrasing, no reversed or Latin-mixed layout artifacts).
This is a minimum quality floor, not a template: keep full creative freedom in design, layout and copy.

Acceptance criteria:
- Implement the task: Implement single-tick update loop
- Cover the task description above.
- Keep the change scoped to what this task needs.
- Do not introduce secrets or credentials in code.
- Leave the repository in a consistent state (no stray debug output).
- User-facing output must satisfy the deliverable quality baseline above (deliberate styling, responsive layout, working interactions).
- The deliverable must be a correct Arabic RTL document (lang="ar", dir="rtl", UTF-8) with polished Arabic content.