fix: Enhance UI Color Palette and Visual Consistency (#616)

[Abhi190702]

Summary

Resolves #616

Changes Made

• Updated core CSS variables (--bg, --surface, --border, --text, --muted)
• Added --accent, --accent-hover, --accent-muted for consistent theming
• Improved button hover/active states with transitions
• Enhanced card styling with shadows and consistent borders
• Replaced hardcoded UI color values with CSS variables where they bypassed the theme
• Improved typography contrast and line-height
• Added consistent focus states on form inputs

Visual Consistency

All changes use the project's approved CSS variable system.
No layout or structural changes were made.

Testing

• bun run lint
• bunx tsc --noEmit
• bun run test
• bun run build

[vercel]

Someone is attempting to deploy a commit to the magic-peach1's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

👋 Thanks for your PR, @Abhi190702!

Welcome to Reframe — a browser-based video editor built for everyone 🎬

What happens next

1. 🤖 Automated checks — build & TypeScript typecheck will run automatically
2. ✅ Vercel preview — a preview deployment will be created (requires maintainer authorization for fork PRs)
3. 👀 Code review — a maintainer will review your changes
4. 🚀 Merge — once approved, your PR will be merged!

Quick checklist

• PR title follows Conventional Commits (e.g. feat: add dark mode)
• Linked the issue this PR closes (e.g. Closes #123)
• Tested the changes locally (bun run dev)
• Build passes (bun run build)

Useful links

• 📖 CONTRIBUTING.md
• 🐛 Open Issues
• ⭐ Star the repo to support the project!

Happy coding! 🎉

[github-actions]

✅ PR Format Check Passed — @Abhi190702

Basic format checks passed. A maintainer will review your code changes.

This does not mean the PR is approved — it just means the format is correct.

[magic-peach]

@Abhi190702 please resolve conflicts