Add connection type validation

[Konstantysz]

Problem

Users can connect incompatible pins (e.g., int output to cv::Mat input), causing runtime errors or crashes.

Proposal

Add compile-time or runtime type checking before allowing connections.

Approach 1 (Runtime)

• Add Slot::GetDataType() -> std::type_index
• Check compatibility in ConnectionManager::TryConnect()
• Show error tooltip if types mismatch

Approach 2 (Compile-time)

• Template Slot<T> with data type
• Type checking via concepts

Future Extension

Auto-insert conversion nodes (e.g., Int→Float adapter).

Acceptance Criteria

• Connecting Mat→int shows error "Type mismatch: cv::Mat cannot connect to int"
• Compatible types (Mat→Mat) connect normally