feat: Component version infrastructure

[tyevco]

Overview

Implement the foundational version tracking infrastructure for component schema migrations.

Parent Issue

• Component Schema Evolution (Phase 16.2) #352 (Component Schema Evolution)
• ADR: docs/adr/015-component-schema-migrations.md

Requirements

Attribute Support

• Add Version property to [Component] attribute (default: 1)
• Validate version is positive integer at compile time

Source Generator

• Generate ComponentMigrationMetadata class
• GetVersion<T>() method for compile-time known types
• GetVersion(Type) method for runtime lookup
• Generate version lookup table (AOT-compatible)

Serialization Format Changes

• Binary format: Add version field (int16) after component type ID
• JSON format: Add $version property to component objects
• Backward compatibility: Treat missing version as v1

Version Mismatch Detection

• Detect version mismatch during deserialization
• Throw ComponentVersionException with clear message
• Include component name, serialized version, current version

Example

[Component(Version = 2)]
public partial struct Health
{
    public int Current;
    public int Max;
    public int Shield;
}

// Generated:
public static partial class ComponentMigrationMetadata
{
    public static int GetVersion<T>() where T : struct, IComponent
    {
        if (typeof(T) == typeof(Health)) return 2;
        // ... other components
        return 1; // default
    }
}

Acceptance Criteria

• Components can declare version via attribute
• Version metadata accessible at runtime (AOT-compatible)
• Serialized data includes version information
• Version mismatch throws descriptive exception
• Unit tests for version metadata generation
• Unit tests for serialization format changes

Technical Notes

• No reflection allowed (Native AOT compatibility)
• Version stored as int16 in binary format (max 32,767 versions)
• Source generator in KeenEyes.Generators