Migrate to k2

[animalet]

Proposed Changes

Note: This is a work-in-progress contribution. I have not worked on IntelliJ plugins before, and the plugin has not been fully end-to-end tested yet. I'm filing this PR in case it helps unblock K2 support, since the repository appears to be unmaintained. Feedback and corrections are very welcome.

Starting from IntelliJ 2025.1, K2 mode is enabled by default. Plugins using K1-only APIs and without a K2 compatibility declaration will not load. This PR migrates the plugin to use PSI-only alternatives and modernizes the build infrastructure.

K1 → PSI migration (zero dependency on the K1 analysis engine):

• findAnnotation(FqName) → annotationEntries + shortName matching
• getKotlinFqName() → KtClassOrObject.fqName (PSI property)
• getReturnTypeReference() → KtNamedFunction.typeReference (PSI property)
• getContainingClass() → PsiTreeUtil.getParentOfType()

K2 compatibility declaration:

• Added <supportsKotlinPluginMode supportsK2="true" /> to plugin.xml
• Bumped since-build to 242 (IntelliJ 2024.2+)
• Made org.jetbrains.android optional with a separate scabbard-android.xml

Build modernization:

• Gradle 7.5.1 → 8.13
• Kotlin 1.6.21 → 2.0.21
• JVM target 1.8 → 17
• IntelliJ SDK 202 → 2024.2
• IntelliJ Gradle Plugin 1.0 → 1.17.4
• Dagger 2.42 → 2.51.1, Dokka 1.5.0 → 1.9.20
• Converted scabbard-gradle-plugin/build.gradle to Kotlin DSL
• Various Gradle 8 / Kotlin 2.0 API migrations

Testing

• ./gradlew :scabbard-idea-plugin:buildPlugin — builds successfully
• ./gradlew :scabbard-idea-plugin:verifyPlugin — passes
• Installed plugin locally in IntelliJ with K2 enabled — no ClassNotFoundException or NoSuchMethodError in IDE logs
• Plugin was not fully end-to-end tested with gutter icon navigation

Issues Fixed

Closes #126

NOTE: The PR has been Vibe coded using Claude Opus 4.6 model