feat: add notification settings and custom thresholds

[Suprita736]

Description

Implemented customizable push notification settings for AQI and individual pollutants, along with quiet hours support.

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Related Issue

Closes #335

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Type of Change

• Bug Fix
• New Feature
• Documentation
• UI/UX Improvement
• Refactoring
• Performance Improvement
• Accessibility

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Changes Made

• Added a Notification Settings panel accessible through the settings/gear button.
• Added customizable AQI alert thresholds.
• Added configurable thresholds for individual pollutants including PM2.5, PM10, NO₂, Ozone, and CO.
• Added Quiet Hours settings to suppress notifications during configured periods.
• Added localStorage persistence for notification preferences.
• Improved the Notification Settings UI for Light Mode, Dark Mode, and High Contrast Mode.
• Improved spacing, alignment, controls, and visual styling while preserving existing notification functionality.

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Testing

• Tested locally
• No console errors
• Existing functionality works as expected
• Light Mode verified
• Dark Mode verified
• High Contrast Mode verified
• Responsive layout verified
• Notification settings persistence verified

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Screenshots

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Checklist

• My code follows the project guidelines.
• I have tested my changes.
• I have updated the documentation if required.
• My changes address the related issue.
• This PR focuses on a single issue.

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Additional Notes

The implementation is limited to Issue #335. Existing notification behavior and unrelated application functionality have been preserved.

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[github-actions]

Thank You for Your Contribution! 🎉

Hi @Suprita736,

Thank you for opening this Pull Request and contributing to our project. We truly appreciate your efforts.

Please make sure that:

• Your code follows the project's guidelines.
• You have linked the appropriate issue (if applicable).
• Screenshots are added for UI/UX changes.
• Your PR is ready for review.

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