fix(ui): Redesign NavDrawer with modern flat sidebar and animated moon/sun theme toggle

[itsofficially-sreyash]

Summary

Redesigns the navigation drawer (NavDrawer) with a cleaner, more modern flat UI that aligns with current Material Design conventions, and replaces the old theme switcher with a smooth animated moon/sun slider toggle.

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Changes Made

• New _ThemeToggleSlider widget — animated pill-style toggle with a sliding thumb that shows a moon icon in dark mode and sun icon in light mode, with color-tinted track and glowing thumb shadow
• New _NavItem widget — flat, consistent nav row with icon + label + subtle chevron; replaces the old NavDrawerMenuItem with a cleaner tap feedback via InkWell
• Refreshed icon set — tune_rounded for Settings, bar_chart_rounded for Reports, logout_rounded for Exit — more semantically accurate
• Tightened header — logo and toggle on the same row, editorial-style bold title, subtle app name label
• Exit button moved to footer — no longer boxed; sits below a divider with red text for clear destructive affordance
• Exit dialog's confirm button is now red for better visual hierarchy

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Before / After

Before	After

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Type of Change

• Bug fix / UI fix
• Refactor (no breaking changes)
• New feature
• Breaking change

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Testing

• Tested on Android
• Tested on iOS
• Light mode verified
• Dark mode verified
• Theme toggle works correctly
• All nav routes navigate as expected
• Exit confirmation dialog works

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Notes for Reviewers

No logic was changed — this is a pure UI refactor. All routes, controller bindings, and language/localization hooks remain identical. The _ThemeToggleSlider is self-contained and can be extracted to a shared widgets folder in a follow-up if needed.