feat: improve balance display, connect button, header user menu, and sidebar active state

[Akpamgbo]

Description

This PR addresses UI and UX improvements across key navigation, header, balance display, and wallet connection components.

Closes #277
Closes #278
Closes #279
Closes #280

Changes proposed

What were you told to do?

• Improve balance-display.tsx with USD equivalent, transaction history link, contract details, and copy action (. Add balance-display.tsx improvements #277)
• Improve connect-button.tsx with wallet detection, network indicator, and account/network switcher dropdown (. Add connect-button.tsx improvements #278)
• Improve header.tsx with user menu dropdown (profile, settings, logout) and notification bell (. Add header.tsx improvements with user menu #279)
• Improve sidebar.tsx with active route highlighting, collapse/expand toggle, and mobile drawer overlay (. Add sidebar.tsx improvements with active state #280)

What did I do?

Balance Display Component

• Added USD equivalent calculation & price conversion display.
• Added 'View Transactions' link navigating to transaction history.
• Added copy-to-clipboard functionality for contract address.
• Added loading state skeleton during price/balance fetch.

Connect Button Component

• Added connected wallet name indicator (Freighter).
• Added network status badge ('testnet' / 'public').
• Added truncated wallet address with instant copy option.
• Added dropdown menu supporting network switching and disconnect options.

Header Component

• Ensured header is sticky on scroll (\sticky top-0 z-50).
• Added user menu dropdown with user avatar, profile link (/profile), settings link (/settings), and logout button.
• Integrated NotificationBell component showing unread notifications.

Sidebar Component

• Implemented active route highlighting using \isNavLinkActive.
• Added collapsible sidebar functionality with toggle button (expand/collapse).
• Added mobile drawer with backdrop overlay that automatically closes on route changes.

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• I am making a pull request against the main branch (left side).
• My commit messages styles matches our requested structure.
• The implementation was reviewed and confirmed to work as intended.
• I am only making changes to files I was requested to.

Screenshots / Validation Evidence

Validated UI components visually and checked responsive layout behavior across desktop and mobile drawer modes.

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