fix: homepage tabs broken, hardcoded playground, docs sidebar not sticky + arrows broken

Describe the bug

Description

Found 3 frontend UI bugs on freeapi.app that affect usability:

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Bug 1: Homepage endpoint tabs are not working

• Clicking the category tabs on the homepage does nothing
• Expected: should filter/show endpoints for that category

Bug 2: Playground is hardcoded

• The API playground always shows the same hardcoded endpoint
• Expected: should dynamically load the endpoint that was clicked

Bug 3: Docs page sidebar issues

• Sidebar is not sticky — when you click a low item you get scrolled far down and have to scroll back up to see the sidebar
• Up/Down arrow buttons in the sidebar are not working
• Expected: sidebar should stay visible (sticky), arrows should navigate between sections

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Steps to Reproduce

1. Go to https://freeapi.app
2. Click any tab on the homepage → nothing happens
3. Open the playground → URL is hardcoded
4. Go to /docs → click a bottom item → sidebar disappears, arrows don't work

I'd like to work on this fix

I'm happy to submit a PR for all 3 of these if this gets approved.

To Reproduce

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Expected behavior

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Screenshots

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OS

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OS Version

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Client

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Additional context or Information

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