fix: rebrand iOS keyboard app to Voxlen #4762

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/voxlen/pull/39

Summary

• Renamed MarcoReidVoiceApp → VoxlenApp
• All UI text: "Marco Reid Voice" → "Voxlen", "AI Voice Dictation for Professionals"
• App Group: group.com.marcoreid.voice → group.ai.voxlen (both main app and keyboard extension)
• Privacy/Terms/Support links: marcoreid.com → voxlen.ai
• Deepgram engine label: "Nova-2" → "Nova-3"
• What's New: updated to reflect legal/accounting smart formatting
• iOS plist usage descriptions: "Marco Reid Voice" → "Voxlen"
• Brand colour: blue → Voxlen purple (#7345d1)

Note for App Store Connect

The Tauri desktop bundle ID (com.marcoreid.voice in tauri.conf.json) still needs updating — recommend doing this alongside setting the iOS Bundle ID in Xcode to match ai.voxlen.keyboard.

https://claude.ai/code/session_011MFNHeFKrhfuSrEYVgrdyr

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