(SP: 2) [Frontend] Add navigation loading states and contextual header behavior

[YNazymko12]

Description

Goal

Improve navigation UX by adding loading states, contextual navigation behavior, and responsive header elements across desktop and mobile.

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Scope

• Add loading indicator for all page transitions (desktop & mobile)

• Update logo behavior:

  • Navigate to the current section (/shop or /blog) instead of always /

• Replace static Home button with contextual section buttons:

  • Show Shop button in shop context
  • Show Blog button in blog context

• Make GitHub stars button responsive:

  • Visible starting from 375px
  • Adaptive sizing across breakpoints

• Improve mobile UX:

  • Add touch interaction states
  • Auto-close mobile menu after navigation

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Expected impact

• Clear feedback during page transitions
• More intuitive navigation behavior
• Improved mobile usability
• Cleaner and more adaptive header UI

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Out of scope

• Backend changes
• Data fetching logic
• GitHub stars API logic