Adopt latest RootPlugin

[alexander-yevsyukov]

This PR updates dependencies on ToolBase and Compiler so that Validation Gradle plugin can add Spine-specific directories via the latest version of RootPlugin.

Documentation changes

• The docs project migrated to hello-validation repository added as a submodule under docs/_examples directory.
• Files in the _script and _settings directories were updated accordingly.
• adding-to-build.md was extended with wording on adding custom plugin repositories.
• adding-to-build.md now has the note on the module script plugin and the link to hello-validation repository.

[Copilot]

Pull request overview

Updates the project to newer Spine toolchain versions and migrates documentation examples to a dedicated _examples submodule, with a small refactor in the Gradle plugin setup.

Changes:

• Bumped Validation/toolchain versions across Gradle, Maven, and buildSrc dependency constants.
• Refactored ValidationGradlePlugin to extract Validation configuration into a helper.
• Migrated docs example sources from docs/_code to a git submodule at docs/_examples and updated embed-code tooling/docs accordingly.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
version.gradle.kts	Bumps the project’s Validation version used by Gradle builds.
pom.xml	Updates Maven artifact and related dependency versions.
gradle-plugin/src/main/kotlin/io/spine/tools/validation/gradle/ValidationGradlePlugin.kt	Refactors plugin application/configuration flow.
docs/content/docs/validation/01-getting-started/first-model.md	Updates getting-started content to reference shared build instructions and refreshed test snippets.
docs/content/docs/validation/01-getting-started/adding-to-build.md	Expands build setup docs and updates plugin versions/snippets.
docs/content/docs/validation/01-getting-started/_index.md	Adjusts navigation/capitalization in the getting-started index.
docs/build.gradle.kts	Points doc automation at _examples and consolidates example build task(s).
docs/_settings/embed-code.yml	Switches embed-code source root from _code to _examples.
docs/_script/embed-code	Updates script comment to reflect _examples submodule usage.
docs/_examples	Adds the examples git submodule pointer.
docs/_code/first-model/src/test/kotlin/io/spine/validation/docs/firstmodel/BankCardKtTest.kt	Removed (migrated to _examples submodule).
docs/_code/first-model/src/test/java/io/spine/validation/docs/firstmodel/BankCardTest.java	Removed (migrated to _examples submodule).
docs/_code/first-model/src/main/proto/spine/validation/docs/first_model/bank_card.proto	Removed (migrated to _examples submodule).
docs/_code/first-model/settings.gradle.kts	Removed (migrated to _examples submodule).
docs/_code/first-model/gradlew.bat	Removed (migrated to _examples submodule).
docs/_code/first-model/gradlew	Removed (migrated to _examples submodule).
docs/_code/first-model/gradle.properties	Removed (migrated to _examples submodule).
docs/_code/first-model/build.gradle.kts	Removed (migrated to _examples submodule).
docs/_code/first-model-with-framework/src	Removed (migrated to _examples submodule).
docs/_code/first-model-with-framework/settings.gradle.kts	Removed (migrated to _examples submodule).
docs/_code/first-model-with-framework/gradlew.bat	Removed (migrated to _examples submodule).
docs/_code/first-model-with-framework/gradlew	Removed (migrated to _examples submodule).
docs/_code/first-model-with-framework/gradle.properties	Removed (migrated to _examples submodule).
docs/_code/first-model-with-framework/build.gradle.kts	Removed (migrated to _examples submodule).
docs/_code/code-common.gradle.kts	Removed (migrated to _examples submodule).
dependencies.md	Regenerates the dependency/license report for the new version set.
buildSrc/src/main/kotlin/io/spine/dependency/local/Validation.kt	Updates referenced Validation runtime/library version.
buildSrc/src/main/kotlin/io/spine/dependency/local/ToolBase.kt	Updates ToolBase version constants.
buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvmCompiler.kt	Updates CoreJvmCompiler version constants.
buildSrc/src/main/kotlin/io/spine/dependency/local/Compiler.kt	Updates Compiler fallback version constants.
.gitmodules	Adds the docs/_examples submodule configuration.

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[Copilot]

Pull request overview

Copilot reviewed 31 out of 31 changed files in this pull request and generated no new comments.

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