Improve Header UI, Fix Theme Switching, and Add Daily Uses

[qwerty274]

📌 Description
This PR improves the Periodic Table Explorer with three main updates:

1. Enhanced Header Design
   Refined the main header with the site favicon, a responsive gradient title, better spacing, and theme-aware styling for a cleaner look in both light and dark mode.

2. Bug Fixes
   Fixed the JSX/build issues in the PeriodicTable component and resolved the theme-switching glitch so the heading and layout update correctly without needing a full page reload.

3. Daily Uses Feature
   Added a new Daily Uses section in the element detail panel to show real-world applications for elements. Currently populated for selected elements like Hydrogen, Helium, Carbon, and Oxygen.

🔗 Related Issue
NSoC'26 Contribution

🚀 Type of Change

• Bug Fix
• Feature
• Enhancement

🧪 Testing

• Verified the header renders correctly in both light and dark mode
• Tested theme switching without page reloads
• Confirmed the element detail panel shows the Daily Uses section
• Checked that the app compiles without console errors

📸 Screenshots

• Header with favicon icon and responsive title
• Element detail panel with Daily Uses section
• Theme toggle in light and dark mode

✅ Checklist

• Code follows guidelines
• Tested properly
• No console errors
• PR title includes NSoC'26

📝 Commits Included

• fix: improve header UI and fix JSX syntax
• feat: add daily uses feature for elements
• fix: stabilize theme switching and icon header

[qwerty274]

kindly check my changes and merge if u feel its okay!!!
thanks regards
also add valid labels to it with nsoc26

[shwetap3000]

@qwerty274
Add the ss of the output and also mention which issue does this pr solve??

[qwerty274]

#55

improved this section in dark mode , also added logo to the pg
there were glitches while switching themes so fixed that
and all other changes are mentioned in the pr above

[shwetap3000]

@qwerty274
resolve the conflicts