feat: sound theme management — select, upload, and preview machine sounds

[hessius]

Summary

Add machine sound management capabilities leveraging the Meticulous API. These features are available via existing API endpoints but not yet exposed in Metic.

Split from #327 (part 1).

API Endpoints

• GET /api/v1/sounds/list — List available sound themes
• POST /api/v1/sounds/set — Set active sound theme
• GET /api/v1/sounds/get/{name} — Get theme details
• POST /api/v1/sounds/upload — Upload custom sound theme
• DELETE /api/v1/sounds/delete/{name} — Delete custom theme
• GET /api/v1/sounds/volume / POST /api/v1/sounds/volume — Get/set volume

Behaviour

A new "Sounds" section in Settings with:

• Dropdown to select active sound theme from installed themes
• Volume slider (0–100%)
• Upload button for custom .zip sound packs
• Delete button for user-uploaded themes (not defaults)
• Preview/play button for each theme

References

• Research: research: MeticulousHome repository analysis — findings & impact for milestones 2.2–2.4 #283
• Original issue: feat: machine management — sound themes, WiFi, and health dashboard #327
• Backend API: meticulous-backend