fix: make vite example channel selection bookmarkable

[oliverlaz]

🎯 Goal

Make the Vite example channel selection bookmarkable and shareable by syncing the active channel with the URL.

🛠 Implementation details

• Read a channel query param in the Vite example and pass it to ChannelList.customActiveChannel.
• Sync the active channel back into the URL with history.replaceState while preserving existing params like token and user_id.
• Fall back to the first channel when customActiveChannel is missing or invalid.
• Add coverage for the customActiveChannel fallback behavior.
• Add the shared matchMedia Jest polyfill and missing React imports needed for the exercised test path.

🎨 UI Changes

N/A. This changes URL state only.

[github-actions]

Size Change: +1 B (0%)

Total Size: 428 kB

Filename	Size	Change
./dist/cjs/index.js	214 kB	+1 B (0%)

ℹ️ View Unchanged

Filename	Size
./dist/audioProcessing-BbOs2wMd.js	1.32 kB
./dist/Channel-iBbX1_YS.js	20.2 kB
./dist/ChannelPreview-CXRaPTt0.js	13.6 kB
./dist/cjs/emojis.js	2.97 kB
./dist/cjs/experimental.js	3.7 kB
./dist/cjs/mp3-encoder.js	1.27 kB
./dist/css/index.css	41.3 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-CxyAOSJp.js	65.2 kB

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