feat(hotkey): HotkeyService wrapping globalShortcut

Task 17 of the slice plan. register() pre-checks
globalShortcut.isRegistered to detect collisions with other
apps (Failure #1 in spec §6.1) and reports the conflict in
the return object so the OllamaBanner-style failure surface
in Task 29 can report it. unregisterAll() runs on app quit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main/services/HotkeyService.ts

@@ -0,0 +1,26 @@
+import { globalShortcut } from 'electron';
+
+export interface HotkeyBinding {
+  accelerator: string;
+  onTrigger: () => void;
+}
+
+export class HotkeyService {
+  private registered: string[] = [];
+
+  register(binding: HotkeyBinding): { ok: boolean; reason?: string } {
+    const accel = binding.accelerator;
+    if (globalShortcut.isRegistered(accel)) {
+      return { ok: false, reason: `${accel} already registered by another app` };
+    }
+    const ok = globalShortcut.register(accel, binding.onTrigger);
+    if (!ok) return { ok: false, reason: `failed to register ${accel}` };
+    this.registered.push(accel);
+    return { ok: true };
+  }
+
+  unregisterAll(): void {
+    for (const a of this.registered) globalShortcut.unregister(a);
+    this.registered = [];
+  }
+}