[feat](trx-frontend-http): add audio WebSocket endpoint with auto-PTT

Add /audio WebSocket endpoint that streams RX Opus frames to the
browser and accepts TX frames back. Browser UI includes RX/TX Audio
toggle buttons with WebCodecs Opus decode/encode and a level indicator.
TX audio automatically engages PTT on start and releases on stop or
WebSocket disconnect.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/Cargo.toml

@@ -15,6 +15,7 @@ serde = { workspace = true, features = ["derive"] }
 serde_json = { workspace = true }
 tracing = { workspace = true }
 actix-web = "=4.4.1"
+actix-ws = "0.3"
 tokio-stream = { version = "0.1", features = ["sync"] }
 futures-util = "0.3"
 bytes = "1"