Add microphone picker and device management features

- Implement `list_input_devices` to retrieve and filter input-capable audio devices.
- Create `MicPickerDialog` for selecting and saving microphone settings.
- Add `set_env_value` function to update .env file with selected microphone index.
- Update UI components to integrate microphone selection functionality.
- Enhance tests for microphone device handling and environment variable management.

bolt_pet/ui/mic_picker.py

@@ -0,0 +1,98 @@
+"""Microphone picker — MIC_DEVICE in .env is a device index most people have
+no way to look up short of running a script. This dialog lists whatever
+sounddevice can actually see, lets you click one, and writes its index back
+to .env so it survives a restart.
+
+The index, not the name, is what gets saved: the same device is commonly
+listed once per host API (MME, DirectSound, WASAPI, WDM-KS, ...) under the
+same or a near-identical name, which makes a bare name an ambiguous pick that
+sounddevice will flatly refuse to resolve (see audio/mic.list_input_devices).
+The index is exact.
+
+The mic is only ever opened once, at startup (see controller.run()), so a
+pick made here still needs a restart before Bolt actually uses it — this
+dialog just makes finding and saving the right device painless, and offers
+to do the restart for you.
+"""
+
+from __future__ import annotations
+
+from typing import Callable, Optional
+
+from PySide6.QtCore import Qt
+from PySide6.QtWidgets import (
+    QDialog, QDialogButtonBox, QHBoxLayout, QLabel, QListWidget,
+    QListWidgetItem, QPushButton, QVBoxLayout,
+)
+
+from ..audio.mic import list_input_devices
+
+_DEFAULT_LABEL = "System default"
+
+
+class MicPickerDialog(QDialog):
+    def __init__(
+        self,
+        get_current: Callable[[], Optional[int]],
+        on_save: Callable[[Optional[int]], None],
+    ):
+        super().__init__()
+        self._get_current = get_current
+        self._on_save = on_save
+
+        self.setWindowTitle("Bolt — select microphone")
+        self.resize(440, 320)
+
+        self._list = QListWidget()
+        refresh_button = QPushButton("Refresh")
+        refresh_button.clicked.connect(self.refresh)
+
+        top = QHBoxLayout()
+        top.addWidget(QLabel("Pick the microphone Bolt should listen on:"))
+        top.addStretch(1)
+        top.addWidget(refresh_button)
+
+        buttons = QDialogButtonBox(QDialogButtonBox.Save | QDialogButtonBox.Cancel)
+        buttons.accepted.connect(self._save)
+        buttons.rejected.connect(self.reject)
+
+        layout = QVBoxLayout(self)
+        layout.addLayout(top)
+        layout.addWidget(self._list)
+        layout.addWidget(buttons)
+
+    def refresh(self) -> None:
+        self._list.clear()
+        default_item = QListWidgetItem(_DEFAULT_LABEL)
+        default_item.setData(Qt.UserRole, None)
+        self._list.addItem(default_item)
+
+        current = self._get_current()
+        selected = default_item
+        try:
+            devices = list_input_devices()
+        except Exception as exc:
+            self._list.addItem(f"Could not list devices: {exc}")
+            devices = []
+
+        for device in devices:
+            item = QListWidgetItem(
+                f"{device['name']}  [{device['hostapi']}]  (#{device['index']})"
+            )
+            item.setData(Qt.UserRole, device["index"])
+            self._list.addItem(item)
+            if current == device["index"]:
+                selected = item
+        self._list.setCurrentItem(selected)
+
+    def _save(self) -> None:
+        item = self._list.currentItem()
+        value = item.data(Qt.UserRole) if item is not None else None
+        self._on_save(value)
+        self.accept()
+
+    def show_refreshed(self) -> None:
+        self.refresh()
+        self.show()
+        self.raise_()
+        self.activateWindow()