Fix mobile track artist centering

[raymondjacobson]

Summary

• Keep the mobile track-page artist names visually centered under the title while still showing user badges in a separate centered badge row.
• Show accepted collaborators in mobile feed track rows as comma-separated artist names, with one-line ellipsis behavior when the row is too long.
• Preserve badges in feed rows for both the owner and accepted collaborators.
• Add focused unit tests for centered artist badge rendering plus artist-name composition.

Test Plan

• /usr/local/bin/node ../../node_modules/.bin/jest src/components/user-link/TrackArtists.test.tsx src/components/lineup-tile/artistNames.test.ts --moduleNameMapper='{"^react-native$":"<rootDir>/../../node_modules/react-native","^@testing-library/react-native$":"<rootDir>/node_modules/@testing-library/react-native"}'
• /usr/local/bin/node ../../node_modules/.bin/eslint --cache --ext=js,jsx,ts,tsx src/components/user-link/UserLink.tsx src/components/user-link/TrackArtists.tsx src/components/user-link/TrackArtists.test.tsx src/screens/track-screen/TrackScreenDetailsTile.tsx src/components/track/TrackCard.tsx src/components/lineup-tile/TrackTile.tsx src/components/lineup-tile/LineupTileMetadata.tsx src/components/lineup-tile/styles.ts src/components/lineup-tile/artistNames.ts src/components/lineup-tile/artistNames.test.ts
• /usr/local/bin/node ../../node_modules/.bin/tsc --noEmit

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Latest commit: 16f0219

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