Milestone: revive GitHub Workflow plugin development

[YunaBraska]

Milestone: active development is back

This PR is the big revival branch for the GitHub Workflow plugin. It moves the project from the old paused state to a current, tested, actively maintained plugin with stronger editor intelligence, workflow execution, cache controls, localization, docs, and release automation.

User-facing highlights

• Adds richer workflow YAML completion, validation, highlighting, references, hovers, and documentation for GitHub Actions fields, contexts, inputs, outputs, permissions, triggers, shells, envs, secrets, local paths, and action metadata.
• Adds workflow dispatch/run support from the IDE, including current-branch defaults, input editing, cancel/delete/rerun actions, job tree UI, job logs, downloads, and cleaner log rendering.
• Improves remote action/workflow resolution with IDE GitHub accounts, Enterprise-aware account fallback, optional env-token fallback, anonymous fallback, caching, refresh actions, and better failure feedback.
• Adds cache review/import/export/delete settings and language override settings.
• Adds top-language resource bundles and extracts plugin UI strings into translations.
• Adds action update hints, suppression review/undo paths, and cleaner quick-fix/icon behavior.
• Migrates docs from docs to doc, updates README/CONTRIBUTING/navigation/specs, and records the major decisions as ADRs.
• Replaces the old paused-development message with active-development messaging.

Engineering and release highlights

• Migrates the build from Kotlin DSL to plain Gradle Java setup with Java 25 tooling and current IntelliJ Platform Gradle Plugin usage.
• Adds broad editor, completion, highlighting, reference, workflow-run, cache, localization, and remote-resolution regression coverage.
• Collapses CI/release automation into one pipeline with one job and one cache.
• Keeps Marketplace publishing unsigned like the previous release path, requiring only PUBLISH_TOKEN for Marketplace publishing.
• Publishes the plugin ZIP to GitHub Packages before Marketplace, then pushes the release commit/tag, then creates the GitHub release from the tag.
• Avoids triggering a second release run from the generated release commit/tag.

Validation

• Local: ./gradlew --no-daemon check verifyPlugin buildPlugin generatePomFileForPluginZipPublication --warning-mode all
• Workflow YAML parsed successfully.
• Workflow shell blocks validated with sh -n.
• Previous PR/push checks passed before the failed publish attempt; the publish failure was caused by missing repository secrets, not test/build failures.

Release notes

Release notes are taken from CHANGELOG.md during the automated release and will be attached to the GitHub release. Marketplace publishing uses the same plugin ZIP produced by the pipeline.