chore(release): prepare 0.2.0

[moonyue-w]

Summary

Prepare the Go SDK for 0.2.0: update the version reported in request headers, move the reviewed timeout change into the dated 0.2.0 changelog entry, and update installation and version-check examples. Keep an empty Unreleased section and preserve the 0.1.0 history.

Why

The release workflow requires the source version and a nonempty changelog entry to match the requested release. This PR prepares those inputs for the coordinated SDK release.

Verification

• make check-version VERSION=0.2.0
• make lint
• make build (includes ./examples/...)
• make test
• make docs-check
• Changelog validation and extraction for 0.2.0; 19 release-notes automation tests passed.
• Account-backed integration tests are not required for this version/documentation-only PR; the source baseline passed integration before the version bump.

Impact

• Runtime version metadata reports 0.2.0; no new API or behavioral changes are introduced here.
• Reviewed user-facing notes moved from Unreleased to 0.2.0 without alteration.
• Generated API documentation and contract fixtures need no changes; documentation checks passed.
• Python and TypeScript release versions are coordinated at 0.2.0.
• Existing timeout guidance remains in the changelog; no additional migration is introduced by this PR.
• No credentials, environment files, logs, or generated test output committed.