feat(agent-teams): add plugin for multi-agent team orchestration

New plugin with 7 presets (review, debug, feature, fullstack, research,
security, migration), 4 specialized agents, 7 slash commands, 6 skills
with reference docs, and Context7 MCP integration for research teams.

plugins/agent-teams/.mcp.json

@@ -0,0 +1,6 @@
+{
+  "context7": {
+    "command": "npx",
+    "args": ["-y", "@upstash/context7-mcp"]
+  }
+}