Add /voice settings to choose a voice for future conversations

[copyberry]

Add /voice settings to choose a voice for future conversations

Why

The TUI has no voice picker, and realtime start requests omit the voice preference. Voice selection also needs to reflect the active project's effective server settings, which can differ from cached local settings.

What changed

• Add /voice settings with the server's voice catalog and current effective selection, falling back to the built-in catalog when unavailable.
• Save realtime.voice through the app server and reread effective settings before confirming the selection. Report save failures and overrides.
• Resolve the effective voice for each realtime start. Apply selections to the next voice conversation without interrupting live audio, and retain compatibility with servers that lack config/read or return unknown voice names.

Testing

Add picker and confirmation snapshots, plus request tests covering persistence, server defaults, catalog fallback, unknown voices, config read failures, overrides, and project settings after thread switches.

[github-actions]

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