chore(release): prepare 0.13.0 - #35

Summary

Prepare 0.13.0 from the merged official-contract and Session metadata changes. Update project and editable-package lock versions without dependency changes; exported runtime metadata now reports 0.13.0 for both sync and async clients.

Move the complete Unreleased notes into the 0.13.0 section, retain an empty Unreleased section, and preserve all breaking-change and migration guidance for Outcome/model types, Identity mounts and reserved Session metadata keys.

Why

The current package version is 0.12.0. This minor release packages the already merged API additions and compatibility changes, and makes SDK request/version markers identify the new release consistently.

Verification

• uv sync --extra dev --locked
• uv run make lint
• uv run make typecheck
• uv run make test (4251 passed; 73 integration cases deselected)
• uv run make docs-check
• uv run make build
• uv run python -m examples.forward --help
• uv run python -m examples.managed --help
• Changelog validation, 0.13.0 release-note extraction and release-automation unit tests
• Account-backed testing scope recorded below

The pre-version source d5a99e0c7d74e68ae19676880818740d37bd90e7 passed internal QA and local package acceptance within the agreed scope. This PR changes version/changelog metadata only; existing offline Session metadata tests verify the current runtime version in the request body and headers. Real-service testing was not repeated on this version branch. After merge, rerun internal integration and produce/accept QA packages from the merged 0.13.0 commit before publishing.

Coverage limits remain: OAuth authorization and OSS access were checked offline only; real channel pairing and Dream execution were excluded. SA execution and Realtime PCM were not included in the internal stable run.

Impact

• Public SDK version metadata advances to 0.13.0; no additional API changes in this PR
• Changelog notes moved from Unreleased to the target release
• Go and TypeScript parity considered; synchronous and asynchronous clients remain aligned
• Existing migration notes retained for the pre-1.0 compatibility changes
• No credentials, .env.live, logs or generated test output committed

Generated API documentation and contract fixtures are unchanged because this PR only advances the version and groups existing notes.

This PR is part of the coordinated Go/Python/TypeScript 0.13.0 release preparation. It does not create a release tag, publish packages, or promote internal main.