feat: add hotkey conflict detection and microphone listing helpers

Implementiere drei Hilfsfunktionen in _settings.py:
- check_hotkey_conflict(): Prüft mit Win32 RegisterHotKey ob eine Taste belegt ist
- list_microphones(): Gibt alle Eingabegeräte als (name, index) Tupel zurück
- pynput_to_evdev_key(): Konvertiert pynput Keys zu evdev Key-Namen

Alle Tests (9 neue + 9 existierende) bestehen.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

whisper_local/tray/_settings.py

@@ -0,0 +1,57 @@
+"""Einstellungs-Dialog für whisper-local (Windows)."""
+
+from __future__ import annotations
+
+import ctypes
+import threading
+from typing import Callable
+
+import sounddevice as sd
+
+from whisper_local.config import Config, save_config
+
+
+def pynput_to_evdev_key(key) -> str:
+    """Konvertiert pynput-Key zu evdev-Key-Namen (z.B. Key.f12 → 'KEY_F12')."""
+    from pynput.keyboard import Key, KeyCode
+
+    if isinstance(key, Key):
+        return f"KEY_{key.name.upper()}"
+    if isinstance(key, KeyCode) and key.char:
+        return f"KEY_{key.char.upper()}"
+    return ""
+
+
+def check_hotkey_conflict(evdev_name: str) -> bool:
+    """Gibt True zurück wenn die Taste per Win32-RegisterHotKey belegt ist."""
+    from whisper_local.hotkey._pynput import _evdev_to_pynput_key
+    from pynput.keyboard import Key
+
+    try:
+        pynput_key = _evdev_to_pynput_key(evdev_name)
+    except ValueError:
+        return False
+
+    if not isinstance(pynput_key, Key):
+        return False
+
+    vk = getattr(pynput_key.value, "vk", None)
+    if vk is None:
+        return False
+
+    HOTKEY_ID = 0x7FFF
+    user32 = ctypes.windll.user32
+    if user32.RegisterHotKey(None, HOTKEY_ID, 0, vk):
+        user32.UnregisterHotKey(None, HOTKEY_ID)
+        return False
+    return True
+
+
+def list_microphones() -> list[tuple[str, int]]:
+    """Gibt Liste aller Eingabegeräte als (name, index) zurück."""
+    devices = sd.query_devices()
+    return [
+        (dev["name"], idx)
+        for idx, dev in enumerate(devices)
+        if dev["max_input_channels"] > 0
+    ]