Microphone stays active permanently (menu bar mic indicator + orange dot) while Hex is running, even when not recording

**Describe the bug**
While Hex runs on macOS, the microphone indicator stays on permanently. The mic icon in the menu bar and the orange dot in the top-right corner stay lit even when no recording is running. Hex appears to keep an audio input stream open in the background instead of acquiring the mic only while recording.

**To Reproduce**
1. Launch Hex and leave it running with no recording active
2. Look at the macOS menu bar mic-usage indicator and the orange privacy dot
3. They stay on continuously, with no recording started

**Expected behavior**
Hex should hold microphone access only while recording and release it the moment recording stops, so the macOS mic indicator and orange dot stay off when idle.

**Desktop**
- Hex 0.7.6 (86)
- macOS 26.5.1

No files or tests are named. Start by locating Hex’s microphone/audio-input stream lifecycle and the recording start/stop entry points; verify that the stream is created only during recording, released immediately after stopping, and leaves the macOS mic indicators off while idle.

Written by the indexing model from the issue text.