feat: replace Tauri with iced for native cross-platform GUI

- Create iced-app crate with pure Rust GUI using iced 0.13
- Implement server list, connect form, channel/user panels, messaging
- Implement ServerQuery panel for direct server queries
- Add VoiceEngine in tsaudio for decode/buffer/playback pipeline
- Update CI to build iced binary (no frontend build step needed)
- Remove Tauri dependency from workspace
- 69 tests passing across all crates

src/Cargo.toml

@@ -5,7 +5,7 @@ members = [
     "tsaudio", 
     "tsdb",
     "shared",
-    "tauri-app/src-tauri",
+    "iced-app",
 ]
 
 [workspace.package]