refactor: remove orphan files and slim FileExplorer to live helpers

[cleanjunc]

Summary

Drops four orphan files that were exported but never imported by any consumer, plus the dead default export of FileExplorer:

• src/pages/DiscoveriesPage.tsx (the /discoveries route is already a redirect, so the page never renders)
• src/components/miners/MinerComparisonRadar.tsx
• src/components/leaderboard/LeaderboardTableSkeleton.tsx
• src/components/common/SearchInput.tsx

buildFileTree and the FileNode type from FileExplorer.tsx are still used by RepositoryCodeBrowser, so they move to a focused fileTree.ts utility module and the lone import is updated. Two small redundancies inside the helper were also collapsed: a duplicated comparator and a recursive resort that produced the same ordering the initial sort already guarantees.

Net effect: roughly 470 lines drop out of the bundle, directories stop advertising features that no longer work, and grep on these component names stops returning orphans.

Related Issues

Closes #976

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Screenshots

Not applicable. No UI or visual changes.

Checklist

• New components are modularized/separated where sensible
• Uses predefined theme (e.g. no hardcoded colors)
• Responsive/mobile checked
• Tested against the test API
• npm run format and npm run lint:fix have been run
• npm run build passes
• Screenshots included for any UI/visual changes

[cleanjunc]

@anderdc Could you please review this PR? Thanks!

[anderdc]

Fix conflicts.

[cleanjunc]

Hi @anderdc
I've fixed the conflicts. Could you please review again?
Thank you!