chore: Remove Renovate and set CODEOWNERS to the sdk team

renovate.json used the deprecated config:base preset and only enabled
updates for @seamapi/types, which Dependabot already covers, so it was
doing nothing that the npm ecosystem in dependabot.yml does not.
Composer dependencies stay under manual control.

Set CODEOWNERS to the sdk team to match the other SDK repositories.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RFK47311nWtbd3gHmjdknR

Author: claude

.github/CODEOWNERS

@@ -1 +1 @@
-* @rchodava @andrii-balitskyi @seveibar
+* @seamapi/sdk