[FEATURE] Add setting to auto-enable voice mode on session start

Currently, voice mode must be manually activated with /voice at the start of every session.

The voiceEnabled: true setting in settings.json makes voice available but doesn't auto-activate it. There's also no CLI flag (like --effort has for effort level).

Request: Add either:

1. A voiceAutoStart: true setting in settings.json, or
2. A --voice CLI flag (so it can be aliased/persisted), or
3. Make voiceEnabled: true actually start the session with voice mode active

This would match how alwaysThinkingEnabled works — set it once, and it's on for every session.

Environment: Windows 11, Claude Code v2.1.75, PowerShell