System Music Notification Toast

Added

• 🦊 NeoForge support (separate JAR, same features as Fabric)
• Multi-loader project structure with shared common code
• Dual JAR release workflow (Fabric + NeoForge published to Modrinth separately)

Changed

• Restructured project to common/fabric/neoforge modules
• Shared runtime logic extracted to SmnToastClientRuntime
• Shared logger extracted to SmnToast class
• Release workflow builds both JARs and publishes to Modrinth with correct loader tags