feat: click now-playing cover/title/artist to navigate (#69)

[klay2000]

Summary

• Clicking the album art or track title in the player bar's now-playing area navigates to that track's album page
• Clicking the artist name navigates to the artist page
• Adds hover styling (pointer cursor, dim/underline) to indicate these are clickable
• Falls back to non-interactive display if albumId/artistId are missing

Closes #69

Test plan

• npm run build passes
• npm test passes (36 tests)
• Manually verified: clicking cover/title opens album page, clicking artist opens artist page

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