Add MiniMax web search MCP to VP Product and CMO agents

- .mcp.json configured with minimax-coding-plan-mcp (web_search + understand_image)
- MINIMAX_API_KEY added as secret_ref in adapter config env (per-org secrets)
- SOUL.md updated with web search usage guidance
- Keys stored in Paperclip secrets, not in repo

Co-Authored-By: Paperclip <noreply@paperclip.ing>

product/.mcp.json

@@ -0,0 +1,12 @@
+{
+  "mcpServers": {
+    "minimax-search": {
+      "type": "stdio",
+      "command": "uvx",
+      "args": ["minimax-coding-plan-mcp", "-y"],
+      "env": {
+        "MINIMAX_API_HOST": "https://api.minimax.io"
+      }
+    }
+  }
+}