fix(api): support delete_memory by user_id/conversation_id (Fixes #1103)#1104

fancyboi999 wants to merge 4 commits intoMemTensor:dev-20260302-v2.0.8MemTensor/MemOS:dev-20260302-v2.0.8from

fancyboi999:fancy/issue-1103-delete-by-user-conversationfancyboi999/MemOS:fancy/issue-1103-delete-by-user-conversationCopy head branch name to clipboard