Standard structure selection for loops over systems

• The "For systems in the database" loop now uses SEAMM's standard structure selection: the systems to loop over (all, the current one, or those whose name is / matches / matches a regular expression) and which configurations of each (last, first, all, the current one, or by name), or a variable holding a list of configurations or systems. The defaults -- every system, its last configuration -- are unchanged, and flowcharts saved with the old options are translated when loaded.
• Bugfix: selecting configurations by "name is" never matched (the name was compared by identity, not equality), and "name matches" / "name regexp" fell through to no selection at all.
• Requires seamm 2026.9.18.1 or later.