chore: enable experimental agent teams via shared settings.json

Adds .claude/settings.json with CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1
so every contributor gets the `team` keyword + TeamCreate tool on clone,
without each person having to set the env var locally.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.claude/settings.json

@@ -0,0 +1,5 @@
+{
+  "env": {
+    "CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS": "1"
+  }
+}