Fix InputVolumeMeters event streaming and optimize v5.x event subscription

[Copilot]

Audio level meters loaded initially but stopped updating. Event subscription included undefined bits. Legacy v4.x event types remained in codebase.

Changes

Critical: Fix audio level streaming

• Manage StreamSubscription lifecycle in DashboardStore - cancel previous before creating new
• Prevents multiple listeners on reconnect that caused event loss
• Add cleanup in stopTimers()

Optimize event subscription bitmask

• 131071 → 67583 (2047 standard + 65536 InputVolumeMeters)
• Remove undefined bits 11-15
• Document bit positions: 2^0 through 2^10 = 2047, 2^16 = 65536

Remove legacy v4.x code

• Delete unused SwitchScenes event type
• Add TODO for ScenesChanged verification

Documentation

• Add troubleshooting section to README with OBS version compatibility matrix
• Document v5.x protocol in NetworkHelper with links to official spec

Example

// Before: Multiple listeners created on reconnect
void handleStream() {
  GetIt.instance<NetworkStore>().watchOBSStream().listen(...);
}

// After: Managed subscription
StreamSubscription? _eventStreamSubscription;
void handleStream() {
  _eventStreamSubscription?.cancel();
  _eventStreamSubscription = GetIt.instance<NetworkStore>().watchOBSStream().listen(...);
}

Event data access patterns verified correct - BaseEvent extracts eventData, BaseResponse extracts responseData. All request parameters confirmed v5.x compliant.

Original prompt

There are .md files for you to work down in this branch. perform all of the work and do not stop until all of the items have been completed.

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