Problem

The free RAMSES build refuses any network above 1000 buses, failing at network reading with

STOP CALL FROM Get buses:
You do not have license for more than  1000 buses. Please contact the authors.

The full version is unlocked by a settings record of the form

$LICENSE <email> <64-hex-character key> ;

There is no way to enter one in the interface. A licensed user has to open the settings
file of every case by hand and paste the record in, which puts a personal key into case
data that is often under version control and shared.

Suggestion

Add a licence entry point to the GUI: two fields, the licensee email and the key, stored
once per installation and injected into the generated command file for every run, so the
key never has to appear in a case file the user edits or shares.

Points to settle:

• Where it lives in the UI. Preferences seems the natural home, next to the existing
  RAMSES settings. A prompt offering to open it when a run fails on the 1000-bus message
  would turn the most confusing failure in the product into a one-click fix.
• How it is stored. The preferences node is my.stepss.StepssUI, so a plain string
  there is readable by anything on the machine. Encrypting at rest is worth doing, though
  note that a desktop application has nowhere truly safe to keep the decryption key, so
  this raises the bar rather than making the key secret. Obfuscation that pretends
  otherwise would be worse than storing it plainly and saying so. Worth brainstorming.
• Migration. Whatever key name is chosen has to be added to PreferenceMigration,
  which copies every key out of the old my.ramses.RamsesUI node, so an installation
  upgraded later does not lose the licence.
• Feedback. Show whether a licence is currently active and which email it is bound
  to. The engine banner prints (Full Version) whether or not a licence is loaded, so it
  cannot be used to tell.
• Validation. The key is 64 hex characters and bound to the email, so a typo can be
  caught at entry rather than surfacing later as a misleading 1000-bus error.

See the companion issue in stepss-python-ui (SPS-L/stepss-python-ui#4) for the API side.
Ideally both read the same stored credential rather than each keeping its own copy.