TTS: speaking overlay + permissions/onboarding polish

[thefourcraft]

Part of the Read Aloud (TTS) epic.

Scope

• Minimal floating 'speaking' indicator (reuse MiniRecorder panel infra) with stop button + progress.
• Ensure Accessibility permission messaging covers selected-text read (one grant already covers AX read + synthetic copy).
• Notifications for empty selection / missing API key / model not downloaded.

Files: Views/Recorder/ (new speaking panel), NotificationManager strings.