docs: README.md split by component

[boolivar]

Greptile Summary

The PR reorganizes the root documentation into component-specific READMEs and configures release-please to update version examples in each new file.

• Replaces detailed component instructions in the root README with links to four focused READMEs.
• Preserves the existing Spock, Cucumber, and Gradle plugin usage guidance in the corresponding component directories.
• Adds all component READMEs to release-please's extra-file list.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
README.md	Replaces embedded component documentation with a concise component index and links to the new READMEs.
jdoc-spock/README.md	Preserves the Spock engine installation, test authoring, compiler, and discovery instructions in a component-specific document.
jdoc-cucumber/README.md	Preserves the Cucumber engine dependency, feature, glue, suite, and execution guidance in a component-specific document.
jdoc-spock-gradle-plugin/README.md	Preserves the Spock Gradle plugin configuration, extension, dependency, and task documentation.
jdoc-cucumber-gradle-plugin/README.md	Preserves the Cucumber Gradle plugin configuration, extension, and task documentation.
release-please-config.json	Extends automated version replacement to all four component READMEs using repository-relative paths.

_{Reviews (2): Last reviewed commit: "docs: headings level updated for gradle ..." | Re-trigger Greptile}