Add DEVC package creation support

[Copilot]

The extension had no way to create DEVC (package) objects, which are fundamental to abapGit repository structure.

Changes

• src/web/create.ts
  • Added createDEVC function: prompts for package name and description, creates a new folder (lowercased name), and writes package.devc.xml in abapGit serializer format
  • Registered DEVC - Package (abapGit) at the top of the artifact type picker in createArtifact

The generated file matches the format already parsed by the artifact tree provider (<CTEXT> for description):

<?xml version="1.0" encoding="utf-8"?>
<abapGit version="v1.0.0" serializer="LCL_OBJECT_DEVC" serializer_version="v1.0.0">
 <asx:abap xmlns:asx="http://www.sap.com/abapxml" version="1.0">
  <asx:values>
   <DEVC>
    <CTEXT>My Package Description</CTEXT>
   </DEVC>
  </asx:values>
 </asx:abap>
</abapGit>

Original prompt

---

This section details on the original issue you should resolve

<issue_title>support creation of DEVC object type for packages</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes support creation of DEVC object type for packages #19

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