style: improve navbar hover underline animation

[pari-dubey1]

Summary [required]

Added a smoother and more modern animated underline hover effect for navbar links to improve visual feedback and overall navigation interactivity.

The underline animation now expands from the center with a 75% width effect, creating a cleaner and more polished UI experience.

Also fixed the mobile hamburger menu visibility issue caused during styling updates.

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Related Issue [required]

Closes #215

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Type of Change [required]

• Bug fix — resolves a broken behaviour
• Feature — adds new functionality
• Data — adds new projects to data/projects.json
• Documentation — updates docs, README, or code comments only
• Style — CSS or visual changes only, no logic change
• Refactor — restructures code without changing behaviour
• Test — adds or updates tests

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What Was Changed [required]

File	Change made
static/style.css	Improved navbar underline hover animation, fixed double underline issue, added centered animation effect, and restored mobile hamburger menu visibility

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How to Test This PR [required]

1. Clone this branch:
   git checkout style/navbar-hover-underline

2. Install dependencies:
   pip install -r requirements.txt

3. Run the app:
   python app.py

4. Open:
   http://127.0.0.1:5000

5. Hover over navbar links and verify:

   • Underline animates smoothly
   • Underline expands from center
   • Underline width remains around 75%
   • No permanent underline remains after hover
   • Mobile hamburger icon is visible

6. Run the tests:
   python tests/test_basic.py

Expected output:

27 passed, 0 failed out of 27 tests

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Test Results [required]

27 passed, 0 failed out of 27 tests

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Screenshots (if UI change)

Before:

After:

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Self-Review Checklist [required]

• I have read CONTRIBUTING.md and followed all guidelines
• My branch name follows the convention: feat/, fix/, docs/, data/, style/, test/
• I have run python tests/test_basic.py and all 27 tests pass
• I have run flake8 . locally and there are no errors
• I have not introduced any print() or console.log() debug statements
• Every new function I wrote has a docstring
• I have not modified files outside the scope of the linked issue
• If I changed the UI, I tested it at 375px (mobile) and 1280px (desktop)
• If I added a project to the dataset, it has all required JSON fields

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Notes for Reviewer

This PR only updates navbar styling and hover interactions. No application logic or backend functionality was modified.

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[pari-dubey1]

@komalharshita Hi! I’ve completed the changes in this PR. Everything has been tested locally and is working properly now.

Could you please review and merge this PR into the main branch when you get a chance? Thank you!