Prepare the 0.2.0 release

[ChoMinGi]

What changed

• Sets the parent, modules, examples, and consumer fixture to 0.2.0 and fixes the reproducible-build timestamp.
• Cuts the dated 0.2.0 changelog entry, updates dependency snippets, and closes the 0.1.x support window.
• Uses release-neutral CI wording and resolves the existing actionlint shell warning.

Why

This is the release commit required before creating the signed v0.2.0 tag. Merging this PR does not publish to Maven Central; publication starts only when that tag is pushed.

Checks

• ./mvnw -B -ntp clean verify
• ./mvnw -B -ntp -Pquality -DskipTests -Djacoco.skip=true -Dmaven.javadoc.skip=true clean verify
• Local install plus Spring AI, LangChain4j, and core/prompt-client consumer verification
• actionlint
• All project and consumer versions resolve to 0.2.0
• No existing v0.2.0 tag, GitHub release, or Maven Central coordinates

After merge, wait for main CI before creating and pushing the signed release tag.