docs(contributing): update JDK requirement and KDoc URLs

[RohithPariki]

Problem

1. docs/CONTRIBUTING.md stated that developers must use JDK 17 based on an outdated AGP requirement from issue AGP 8.1.0 requires the developer to use JDK 17 on Gradle JDK #74 ([FR]: Update stale JDK version requirement in CONTRIBUTING.md #2107).
2. catalog/src/main/kotlin/com/adevinta/spark/catalog/util/Url.kt pointed DocsUrl and PackageSummaryUrl to adevinta.github.io/spark-android which causes 404s/wrong project links instead of the current leboncoin.github.io/spark-android deployment ([FR]: Fix KDoc URL pointing to wrong GitHub org in README #2105).

Root Cause

• AGP has since been updated to 9.x (and CI runs on modern JDKs), making the hardcoded link to issue AGP 8.1.0 requires the developer to use JDK 17 on Gradle JDK #74 stale and misleading.
• KDoc hosting moved to the leboncoin GitHub organization when repository ownership transitioned.

Solution

• Updated docs/CONTRIBUTING.md to directly specify that JDK 17 or later is required to build the project and run the Gradle daemon, removing the stale issue AGP 8.1.0 requires the developer to use JDK 17 on Gradle JDK #74 reference.
• Updated DocsUrl and PackageSummaryUrl in Url.kt to point to https://leboncoin.github.io/spark-android and https://leboncoin.github.io/spark-android/spark.

Testing

• Verified Markdown formatting in docs/CONTRIBUTING.md.
• Verified URL validity in Url.kt.

Risk

Zero runtime risk; documentation and catalog link update only.

Issue

Closes #2107
Closes #2105