fix: standardize on file extension .yaml instead of a mix of yml and yaml

bmad-core/agent-teams/team-fullstack.yaml

@@ -0,0 +1,18 @@
+bundle:
+  name: Team Fullstack
+  icon: 🚀
+  description: Team capable of full stack, front end only, or service development.
+agents:
+  - bmad-orchestrator
+  - analyst
+  - pm
+  - ux-expert
+  - architect
+  - po
+workflows:
+  - brownfield-fullstack
+  - brownfield-service
+  - brownfield-ui
+  - greenfield-fullstack
+  - greenfield-service
+  - greenfield-ui