[TASK-13] Audio & All System Feedback #125

Description: Implement AudioManager (subscribes to EventBus, triggers SFX stubs), wire all visual feedback animations (HP flash, damage popup, skill activation), and verify real-time mic feedback on the power bar. The goal is that every game-state change is communicated through at least one sensory channel.

Task Acceptance Criteria:

• AudioManager subscribes to 5+ events and calls playSFX(named:) without crashing on any event.
• HP bar flashes red on damage and green on heal over 0.4s.
• Damage popup floats 50px upward and fades to 0 alpha over 1s.
• PowerBarNode color transitions are smooth (not snapping) with each mic buffer update.
• All SFX file names are documented for audio production handoff.

Prerequisites: TASK-11 (UISystem, HUDNode), TASK-01 (EventBus), TASK-04 (VoiceInputSystem).