fix: prevent today's notes from showing as yesterday

[KARTIK001-CODER]

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Description

Fixes incorrect relative date calculation where notes created today were displayed as “Yesterday” due to timezone shifts and use of Math.ceil().

The logic now compares local calendar days instead of raw millisecond differences.

Fixes #61

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Type of change

• Bug fix (non-breaking change which fixes an issue)

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How Has This Been Tested?

1. Created notes using new Date().toISOString() at different times of day.
2. Verified that notes created today always display as “Today”.
3. Tested behavior across different system timezones.

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Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

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