Add AGENTS.md for Cursor Cloud development environment setup

[jboileau99]

Description of this change

Adds AGENTS.md with Cursor Cloud specific development environment instructions for the Ketch Android SDK. This file provides future cloud agents with the necessary context to build, test, and lint the project without trial and error.

Why is this change being made?

• Chore (non-functional changes)

This is a non-functional addition of developer documentation for automated cloud agent environments.

How was this tested? How can the reviewer verify your testing?

The full development environment was set up and verified:

• JDK 17 installed and configured
• Android SDK (platform 36, build-tools 36.0.0) installed
• All 4 modules built successfully (./gradlew assembleDebug)
• Unit tests pass (./gradlew :ketchsdk:test)
• Ktlint passes (./gradlew ktlintCheck)
• Android Lint passes (./gradlew :ketchsdk:lintDebug)

Build verification log:
build_verification.log

Checklist

• I have added tests to cover my changes.
• All new and existing tests passed.
• I have evaluated the security impact of this change, and OWASP Secure Coding Practices have been observed.
• I have informed stakeholders of my changes.

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