Align the Rust, TypeScript, and Python package versions at 0.12.3.
Document the complete MCP workflows and follow-up contract and read-binding
fixes in the changelog. Update both landing-page languages and the 41-tool
inventory, and clarify the unchanged connector snapshot format in SDK docs.

Validated the three SDK test suites, TypeScript build, Rust lint, shared
catalog parity, Mail interoperability, and bilingual browser demos.

Co-authored-by: Codex <noreply@openai.com>