Fix IntelliJ 2026.1 compatibility and Context Mapper setup

[skurlow]

Summary

• configure the Context Mapper language server to use the stable context-mapper-dsl language ID and improve Node executable resolution
• verify and widen the supported IntelliJ build range for IU 261 after plugin verification passes
• document setup for the Context Mapper plugin, PlantUML, Graphviz, and generating .puml diagrams from .cml files
• add the GitHub Packages registry mapping needed by the bundled language-server package during local builds

Verification

• ./gradlew test
• ./gradlew ktlintCheck
• ./gradlew verifyPluginStructure
• ./gradlew verifyPlugin
• Plugin verification passed against installed IntelliJ build IU-261.25134.95; report generated at build/reports/pluginVerifier/IU-261.25134.95/report.html

Compatibility notes

• ideaUntilBuild is updated from 251.* to 261.* only after verification against IU-261.25134.95
• Node resolution now honors CONTEXT_MAPPER_NODE, then common Homebrew/system Node paths, then falls back to node on PATH
• The Gradle wrapper was updated from 8.11.1 to 8.14.4 so local build and verifier tasks run on the same wrapper version used during this compatibility verification pass
• PlantUML rendering may require Graphviz/dot to be installed and configured separately, for example with brew install graphviz on macOS

Known caveats

• Gradle reported npm audit warnings in the LSP package dependency tree during local verification; these did not block plugin build or verification

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud