Implement Sound Feature or Remove Field

[lowhung]

Description

The sound_enabled field exists but is unused. Either implement audio feedback for graph events or remove the field.

Option A: Implement Sound

• Play subtle sounds on node firing
• Audio feedback for critical health status
• Use rodio or similar crate

Option B: Remove Field

• Remove sound_enabled from NeuronicApp
• Remove from UIPreferences if issue Decompose NeuronicApp into Sub-Structs #39 is completed

Acceptance Criteria

If implementing:

• Add audio crate dependency
• Implement sound effects for key events
• Add UI toggle for sound
• Default to disabled

If removing:

• Remove field and any related code
• Update any UI that references it