Add input device selection to interactive config TUI

Enumerates available audio input devices via cpal and presents them
in a dropdown, with "System default" as the first option.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/cli/config_cmd.rs

@@ -1,4 +1,5 @@
 use anyhow::Result;
+use cpal::traits::{DeviceTrait, HostTrait};
 use dialoguer::{Input, Select};
 use std::time::Duration;
 
@@ -105,6 +106,8 @@ pub fn interactive() -> Result<()> {
         .interact()?;
     config.audio_feedback = feedback_idx == 0;
 
+    config.input_device = prompt_input_device(config.input_device.as_deref())?;
+
     let vad_idx = Select::new()
         .with_prompt("VAD (voice activity detection)")
         .items(&["enabled", "disabled"])
@@ -122,6 +125,52 @@ pub fn interactive() -> Result<()> {
     Ok(())
 }
 
+/// Prompt the user to select an audio input device from available devices.
+fn prompt_input_device(current: Option<&str>) -> Result<Option<String>> {
+    let current_label = current.unwrap_or("system default");
+
+    let host = cpal::default_host();
+    let mut device_names: Vec<String> = Vec::new();
+
+    if let Ok(devices) = host.input_devices() {
+        for device in devices {
+            if let Ok(name) = device.name() {
+                device_names.push(name);
+            }
+        }
+    }
+
+    // Build selection list: "System default" first, then each detected device
+    let mut items: Vec<String> = vec!["System default".to_string()];
+    for name in &device_names {
+        items.push(name.clone());
+    }
+
+    // Find the default selection index
+    let default_idx = if let Some(cur) = current {
+        let cur_lower = cur.to_lowercase();
+        device_names
+            .iter()
+            .position(|n| n.to_lowercase().contains(&cur_lower))
+            .map(|i| i + 1) // offset by 1 for "System default"
+            .unwrap_or(0)
+    } else {
+        0
+    };
+
+    let sel = Select::new()
+        .with_prompt(format!("Input device (current: {current_label})"))
+        .items(&items)
+        .default(default_idx)
+        .interact()?;
+
+    if sel == 0 {
+        Ok(None)
+    } else {
+        Ok(Some(device_names[sel - 1].clone()))
+    }
+}
+
 /// Prompt the user to either press a key combination or type it manually.
 fn prompt_hotkey(label: &str, current: &str) -> Result<String> {
     let choice = Select::new()