feat: align iconOnly API and unread badge styling

[oliverlaz]

🎯 Goal

Align the ChatView selector prop naming with other SDKs and include the unread badge styling updates needed for the threads selector.

Related ticket: REACT-844

🛠 Implementation details

• rename the selector API from showLabels to iconOnly, keeping the default behavior as icon-only
• update the ChatView selector tests and the Vite example settings flow to use iconOnly
• add unread badge styling into the source Threads styling entrypoint and wire it into the main styling index
• stop double-importing the dist unread badge styles in the Vite example stylesheet imports

🎨 UI Changes

The threads selector badge uses the new source unread badge styling, and the selector API now matches the iconOnly naming used in other SDKs.
No screenshots attached.

[github-actions]

Size Change: +256 B (+0.06%)

Total Size: 416 kB

Filename	Size	Change
./dist/cjs/index.js	212 kB	+1 B (0%)
./dist/css/index.css	38 kB	+255 B (+0.68%)

ℹ️ View Unchanged

Filename	Size
./dist/audioProcessing-BbOs2wMd.js	1.32 kB
./dist/Channel-MhCKe2pq.js	20.9 kB
./dist/ChannelPreview-CqYTq6Ri.js	8.82 kB
./dist/cjs/emojis.js	2.97 kB
./dist/cjs/experimental.js	3.62 kB
./dist/cjs/mp3-encoder.js	1.27 kB
./dist/css/v2/emoji-mart.css	1.84 kB
./dist/css/v2/emoji-replacement.css	300 B
./dist/css/v2/index.css	39.4 kB
./dist/css/v2/index.layout.css	22.8 kB
./dist/limits-DuUuDo7N.js	63.4 kB

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