docs(upgrading): add the v18.2.0 row to the per-release table

The "Per-release specifics" table stopped at v18.1.0 although the
18.2.0 release page ships its own upgrade checklist. Add the row above
v18.1.0, pointing at /docs/releases/v18/18-2#upgrade-checklist.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JQwxbWQbmPGoJDwc2QWoUJ

Author: claude

content/docs/upgrading.mdx

@@ -463,6 +463,7 @@ the protocol-18 step, which `os migrate meta --from 17` lists for your sources
 
 | Release | Where its upgrade notes live |
 | :--- | :--- |
+| v18.2.0 | [Upgrade checklist — 18.2.0](/docs/releases/v18/18-2#upgrade-checklist) |
 | v18.1.0 | [Upgrade checklist — 18.1.0](/docs/releases/v18/18-1#upgrade-checklist) |
 | v18.0.0 | [Upgrade checklist — 18.0.0](/docs/releases/v18/18-0#upgrade-checklist) · [Upgrading to 18.0](#upgrading-to-180) (the ownership ceremony) · [v18](/docs/releases/v18) |
 | v17.7.0 | [Upgrade checklist — 17.7.0](/docs/releases/v17/17-7#upgrade-checklist) |