Add Linux audio capture module with unsupported functionality

- Introduced a new `linux.rs` module for audio capture, indicating that audio capture is not supported on Linux at this time.
- Updated `mod.rs` to include the Linux module conditionally based on the target OS.

tauri/src-tauri/src/audio_capture/linux.rs

@@ -0,0 +1,16 @@
+use crate::audio_capture::AudioCaptureState;
+
+pub async fn start_capture(
+    _state: &AudioCaptureState,
+    _max_duration_secs: u32,
+) -> Result<(), String> {
+    Err("Audio capture is not supported on Linux, YET. Use the built-in recording features instead.".to_string())
+}
+
+pub async fn stop_capture(_state: &AudioCaptureState) -> Result<String, String> {
+    Err("Audio capture is not supported on Linux.".to_string())
+}
+
+pub fn is_supported() -> bool {
+    false
+}

tauri/src-tauri/src/audio_capture/mod.rs

@@ -2,11 +2,15 @@
 mod macos;
 #[cfg(target_os = "windows")]
 mod windows;
+#[cfg(target_os = "linux")]
+mod linux;
 
 #[cfg(target_os = "macos")]
 pub use macos::*;
 #[cfg(target_os = "windows")]
 pub use windows::*;
+#[cfg(target_os = "linux")]
+pub use linux::*;
 
 use std::sync::{Arc, Mutex};