docs: explain intentional CartSummary instability

[himattm]

Summary

• Clarifies that CartSummary is intentionally not a data class in the demo
• Explains that the unstable identity-equality behavior is a fixture for Dejavu's recomposition detection examples/tests
• Tells automated agents not to optimize the sample by converting it to a data class

Test Plan

• JAVA_HOME=/opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk/Contents/Home ./gradlew -q --console=plain :dejavu:jvmTest :dejavu:testDebugUnitTest apiCheck
• JAVA_HOME=/opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk/Contents/Home ./gradlew -q --console=plain :dejavu:iosSimulatorArm64Test :dejavu:wasmJsBrowserTest

[gemini-code-assist]

Code Review

This pull request updates the documentation comments for the CartSummary class in ProductList.kt to clarify that its lack of structural equality is intentional for testing the Dejavu library. The review feedback suggests using more idiomatic Kotlin Multiplatform terminology, such as referencing Any.equals() instead of Object.equals(), and refining the description of Compose recomposition behavior.

[gemini-code-assist]

In Kotlin Multiplatform (commonMain), it is more idiomatic to refer to Any.equals() or "referential equality" rather than the JVM-specific Object.equals(). Additionally, since all properties are val and of stable types, this class is technically "Stable" in Compose terms; the recompositions occur due to the lack of structural equality, not type instability. Using "behavior" or "identity equality" instead of "unstable" avoids confusion with the Compose compiler's stability system.

Suggested change

	// INTENTIONAL: regular class with identity-based equality (Object.equals).
	// Keeping this unstable is part of the demo/test fixture; changing it to a
	// INTENTIONAL: regular class with identity-based equality (Any.equals).
	// Keeping this behavior is part of the demo/test fixture; changing it to a