feat(tui): add audio notification system for completion and approval events (#549)

- Add rodio dependency for cross-platform audio playback
- Create sound.rs module with channel-based audio thread architecture
- Embed WAV files for response completion and approval notification sounds
- Play completion sound when streaming response finishes
- Play approval sound when tool approval is requested
- Graceful fallback to terminal bell when audio unavailable

Author: echobt

Cargo.lock

@@ -379,6 +379,7 @@ sysinfo = "0.32"
 hex = "0.4"
 urlencoding = "2.1"
 pin-project-lite = "0.2"
+rodio = { version = "0.19", default-features = false, features = ["wav"] }
 
 [workspace.lints.rust]
 unsafe_code = "allow"

Cargo.toml

@@ -65,6 +65,9 @@ walkdir = { workspace = true }
 # External editor
 which = { workspace = true }
 
+# Audio notifications
+rodio = { workspace = true }
+
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"