fix(opencode): add full MCP path to opencode.json URL

Security Auditor FINDING-1: bare ${MOLECULE_MCP_URL} missing the router path.
Fix adds /workspaces/${WORKSPACE_ID}/mcp so opencode reaches MCPHandler.
Unblocks PR#842 merge.

org-templates/molecule-dev/opencode.json

@@ -2,7 +2,7 @@
   "mcpServers": {
     "molecule": {
       "type": "remote",
-      "url": "${MOLECULE_MCP_URL}",
+      "url": "${MOLECULE_MCP_URL}/workspaces/${WORKSPACE_ID}/mcp",
       "headers": { "Authorization": "Bearer ${MOLECULE_MCP_TOKEN}" },
       "description": "Molecule AI A2A orchestration — delegate_task, list_peers, check_task_status"
     }