v0.1.0-W (vc=10): U-4 + U-5 — channels via rustypipe + rip NewPipeExtractor

channel_info(url) UniFFI suspend fn. ChannelViewModel +
SubscriptionFeedViewModel both swap. NewPipeExtractor (Java) is OUT —
zero org.schabi.newpipe classes in the APK now.

Cleanup:
- NewPipeDownloader.kt deleted (was the OkHttp adapter)
- Thumbnails.kt deleted (rustypipe returns full URLs)
- NewPipe.init() dropped from StrawApp.onCreate
- libs.newpipe.extractor removed from build.gradle.kts
- STRAW_USER_AGENT + strawHttpClient() now live in net/Http.kt
- RydClient + SponsorBlockClient + PlayerScreen + PlaybackService all
  read from net/Http.kt instead of the extractor package

rustypipe API quirks beat:
- channel_videos(id) is the right method (channel() doesn't exist)
- ChannelInfo struct = basic metadata; Channel<T> wrapper carries
  name/avatar/banner + .content is the paginator of videos
- description is String (not Option), subscriber_count is Option<u64>

End state: strawApp Kotlin is ~UI + thin glue to strawcore. The Rust
core handles search / streamInfo / channel / channel_videos via UniFFI
suspend fns. Tokio + reqwest + rustls + rquickjs all packed in
libstrawcore.so (~6MB per ABI). APK 40MB total.

strawApp/build.gradle.kts

@@ -94,8 +94,8 @@ dependencies {
     implementation(libs.coil.compose)
     implementation(libs.coil.network.okhttp)
 
-    // NewPipeExtractor (JVM/Android-only) + its OkHttp dep
-    implementation(libs.newpipe.extractor)
+    // Phase U-5: NewPipeExtractor (Java) torn out — strawcore handles
+    // all YT extraction. OkHttp stays for RYD + SponsorBlock JSON clients.
     implementation(libs.squareup.okhttp)
 
     // JSON for SponsorBlock + Return YouTube Dislike clients