chore: retarget plugin compatibility to IntelliJ IDEA 2023

[Idddd]

Motivation

• Narrow plugin compatibility to the IntelliJ 2023 release line so the project supports 2023.x IDEs and no longer targets 2025.

Description

• Set platformVersion to 2023.3 in gradle.properties to use the IntelliJ 2023 platform.
• Adjusted patchPluginXml bounds in plugin-idea/build.gradle.kts to sinceBuild = "231" and untilBuild = "233.*" to limit the plugin to 2023 builds.
• Updated README badges and installation/development prerequisites to reference IntelliJ IDEA 2023.3+.
• Modified README.md, gradle.properties, and plugin-idea/build.gradle.kts accordingly.

Testing

• Attempted ./gradlew :plugin-idea:buildPlugin --no-daemon which failed in this environment due to a missing Gradle wrapper main class (org.gradle.wrapper.GradleWrapperMain), so a full build could not be validated automatically.

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Codex Task