AI review

Summary: Refactoring to extract delete logic into a static method process_delete for future FastAPI migration.
Changes:

• Moved cache invalidation and delete document save from POST method to new @staticmethod process_delete
• All tests and checks pass ✓
  Potential Risks:

1. Minimal risk - This is a straightforward refactor. Logic is preserved:
   • Cache key: "core.patron_lists.%s" % web.safestr(doc.key)
   • Delete doc: {"key": key, "type": {"key": "/type/delete"}}
   • Save with action="lists" and comment="Deleted list."
2. Static method constraint - The method uses web.ctx.site (global context) rather than instance state, so making it static is appropriate.
3. No error handling change - The try/except in POST still catches ClientException from process_delete.
   Verdict: Safe to merge. The refactoring is clean and maintains identical behavior.