docs: add September 28 MCP release notes

[yechang15]

Summary

• Add a date-only 2026-09-28 release entry covering production-verified Python MCP SDK 2.2.0 OAuth compatibility and released agent-plugin monitoring guidance.
• Link bug(mcp): Python SDK 2.2.0 OAuth fails before browser authorization call-e-integrations#155 and Align MCP skill guidance for terminal aliases and next_step instructions awesome-phone-call-agents#770.
• Keep historical content unchanged and exclude unverified fixes.

Evidence

• OAuth production verification is recorded in integrations #155 and related merged PR #157.
• Plugin guidance shipped via integrations PRs #146 and #142 (Claude 0.2.4, Codex 0.1.13, Cursor 0.1.3).
• This describes plugin instructions, not a new CLI polling implementation or a guarantee of every host behavior.

Validation

• Full pnpm run validate passed, including all 32 Playwright tests.
• git diff --check passed.

No release needed: documentation and test updates only; no package bump or changeset required.