Clarify merge review and remove release artifact quota dependency

[jakezwang]

SDK examples applied merges immediately while describing a separate review step, and publication depended on Actions artifact storage that can block releases when the account quota is exhausted.

• Show merge preview, plan inspection and explicit apply in client, LangGraph and Mem0 examples. Document that convenience merge() still previews and applies immediately, and scope undo/pin claims to retained captured state.
• Validate the requested release tag against its package version and main-branch ancestry. Pass its exact commit SHA to publication, revalidate it, then rebuild and check wheel/sdist before uploading directly to PyPI. Build failures, publication failures and actual registry verification remain required; no Actions artifact transfer is needed.

Validation: all 8 integration tests passed against engine 2.1.1 and MongoDB 7; remote CI passed Python 3.10, 3.12 and 3.14 before the workflow-only follow-up. Actionlint passed both workflows. The exact v0.2.0 tag rebuilt locally, both distributions passed Twine, and installed wheel imports passed outside the checkout. Workflow checks confirmed identical distribution build/check commands, required gates and rejection of a mismatched release SHA. git diff --check passed.

Runtime API behavior, package version and existing GitHub release assets are unchanged. Actual PyPI publication still requires the configured publisher and is verified separately by the workflow.