chore(release): prepare 0.4.0 for Service Account support

[moonyue-w]

Summary

Update package, lockfile root package and exported VERSION to 0.4.0, refresh the release command example and regenerate VERSION documentation. Move existing SA release notes and migration guidance into the 0.4.0 changelog section.

Why

Prepare the next coordinated SDK release containing the already merged renewable Service Account authentication, direct SAT support and authentication examples. Version metadata and reviewed release notes must match before dispatching the release workflow.

Verification

• npm run build
• npm run typecheck
• npm test
• npm run docs:check
• Relevant examples run or import successfully
• Account-backed integration tests run, or not required

Commands and results:

npm test
npm run typecheck
npm run docs:check
npm pack --ignore-scripts
All passed; 3,505 offline tests passed.
An independent tgz consumer verifies 0.4.0, SA exports, CJS/ESM and Forward/Managed subpaths.

python3 .github/scripts/release_notes.py check
python3 .github/scripts/release_notes.py extract --version 0.4.0
python3 -m unittest discover -s .github/scripts -p 'test_*.py'
All passed; 19 release-automation tests per repository.

Impact

• Public API or behavior changed
• User-facing changes added to CHANGELOG.md under Unreleased, or not applicable (explain below)
• CommonJS, ESM, and subpath exports remain valid
• Generated API documentation updated
• Contract or wire-field fixtures updated
• Go and Python parity considered
• Migration notes added for a breaking change
• No credentials, .env.live, logs, or generated test output committed

Additional context:

This is a release-metadata PR; endpoint contracts and SDK runtime behavior are unchanged. Existing SA migrations are retained in the versioned notes. The generated VERSION reference is updated. Example smoke checks were not repeated for unchanged examples. The merged SA implementation has prior CN/Global read, write, SSE and cleanup verification; live tests were not rerun for this metadata-only bump. The TypeScript release also includes the merged Batch E2E idle-window test correction (#14).