[Feature] Migrate workflow definitions to .kts with global IDE support

[alxsuv]

Description:

Context

Currently, workflow definitions are authored in standard .kt files. We are moving to Kotlin Script (.kts) files to provide a cleaner, boilerplate-free DSL. While the Kotlin compiler already successfully
processes these scripts with implicit imports and DSL receivers, IntelliJ IDEA lacks the context to resolve them. This results in false-positive "unresolved reference" (red code) errors in the editor. We need to
configure the Kotlin Scripting environment so the IDE properly understands the DSL context globally across the project.

Goals

• Migrate existing workflow definitions from .kt to .kts (e.g., *.workflow.kts).
• Provide seamless, auto-resolving IDE support (syntax highlighting, autocomplete) for workflow scripts in IntelliJ.
• Ensure the script definition is globally recognized anywhere in the repository, not just within a specific dsl package.
• Achieve a developer UX identical to build.gradle.kts (no boilerplate imports, implicit receivers pre-configured).

Non-goals

• Modifying the underlying execution semantics or compiler logic of the workflows.
• Building custom IDE plugins from scratch (we should rely on standard JetBrains Kotlin scripting support).
• Expanding support to non-JetBrains IDEs in this iteration.

Acceptance criteria

• Existing workflow files are renamed to the new *.workflow.kts extension and stripped of boilerplate.
• Opening a *.workflow.kts file anywhere in the project tree in IntelliJ displays no red code / unresolved reference errors.
• Implicit DSL receivers and standard imports are automatically available in the IDE context.
• Autocomplete functions correctly for the workflow DSL.
• The IDE automatically discovers the script configuration without requiring manual user setup per file.

Implementation notes

• Leverage kotlin-scripting-jvm and kotlin-scripting-jvm-host artifacts to establish the script definition environment.
• Create a custom @KotlinScript annotation with a ScriptCompilationConfiguration supplying implicit receivers and default imports to the IDE.
• Use KotlinScriptHostConfiguration if needed to bridge classpath resolution.
• Register the script definition's FQN in META-INF/kotlin/script/templates/ for IDE auto-discovery.
• Mirror Gradle's .gradle.kts wiring so the definition is available globally regardless of package depth.