fix(a11y): resolve WAVE audit control issues

[saurabhhhcodes]

Fixes #178

Summary

• add programmatic names for hidden upload/search controls so WAVE and screen readers do not see unlabeled inputs
• mark decorative icons/ratio boxes as hidden and add pressed states to preset, overlay, and text-selection controls
• replace the orphaned text weight legend with a real fieldset and add clearer trim-slider instructions/value text
• tighten light-theme muted/accent/warning/error tokens to pass WCAG AA contrast on white and surface backgrounds

Verification

• npm run lint (passes; existing VideoEditor exhaustive-deps warning remains)
• npx tsc --noEmit
• npm run build (passes; same existing warning)
• token contrast sanity check: muted/accent/warning/error pairs are now >= 4.5:1 on light backgrounds

Note: I also attempted an axe CLI run against the static build, but the local ChromeDriver bundled by the tool only supports Chrome 149 while this workstation has Chrome 148, so that browser audit could not run locally.

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[github-actions]

👋 Thanks for your PR, @saurabhhhcodes!

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• 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)
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[github-actions]

✅ PR Format Check Passed — @saurabhhhcodes

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[saurabhhhcodes]

Hi maintainers, this is for assigned issue #178. Could you please add gssoc:approved and type:accessibility during review if the scope looks right?

Local verification completed:

• npm run lint (passes; existing VideoEditor exhaustive-deps warning remains)
• npx tsc --noEmit
• npm run build
• contrast sanity check for light-theme muted/accent/warning/error tokens, all now >= 4.5:1 on white/surface backgrounds

Vercel is showing the usual fork authorization status, not a code failure.

[saurabhhhcodes]

Closing this older duplicate in favor of #1489, which covers the same #178 accessibility scope with the cleaner/current patch and better label coverage. Keeping one PR open for review to avoid duplicate maintainer work.