Fix double URL-encoding of Spotify search queries

[d1r0l]

Summary

• searchAsync was encoding the query twice — once manually via encodeURIComponent, once again via `URLSearchParams`'s own encoding — corrupting any query with non-ASCII or special characters before it reached Spotify's Search API.
• Removes the redundant manual encoding; URLSearchParams already encodes its values correctly on its own.

Fixes #104

Test plan

• npm test — all existing suites pass
• npm run build — compiles clean
• Manually verified in Firebot: searching a Cyrillic query that previously returned unrelated results now returns the correct match