[FR]: Update stale JDK version requirement in CONTRIBUTING.md

Describe the problem

CONTRIBUTING.md says "We currently use a version of AGP which requires developers to use JDK 17" and links to issue #74. Build logic targets JVM 11 for most modules and JVM 21 for multiplatform. The JDK 17 claim is tied to an old issue and may not reflect the current minimum with AGP 9.x.

Describe the solution

• Verify the current minimum JDK for running the Gradle daemon
• Remove the outdated issue #74 link
• State the requirement directly (e.g. "JDK 17 or later is required to build the project")

Additional context

Priority: High. Effort: XS.