Port QConnect to self-contained prost implementation

Replaces qbz path-dependencies with a standalone implementation using
tokio-tungstenite and prost. Fixes queue-clear sentinel handling, pause
position reporting, track-end queue advancement, and adds periodic
position progress reports to keep the app progress bar in sync.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.toml

@@ -33,6 +33,7 @@ sha1 = "0.10"
 hex = "0.4"
 tokio-tungstenite = { version = "0.24", features = ["native-tls", "native-tls-vendored"] }
 futures-util = "0.3"
+prost = "0.13"
 symphonia = { version = "0.5", features = ["flac", "pcm", "mp3", "aac", "ogg", "wav"] }
 cpal = "0.15"
 rubato = "0.15"