jmsfx-creator has no tests

[ctgnz]

What

jmsfx-creator has no tests at all - no src/test, and no test dependencies in its pom. #63 was a real bug in it that went unnoticed, and the only way to confirm the fix was a throwaway probe calling the private method by reflection. That should be a test.

Why it is worth doing

The logic worth covering is not the UI. It is the plain bookkeeping the creator does around it, which is where #63 lived:

• rebuilding the entity, entity type, entity subtype, amplifier and sector modifier lists when the symbol set, entity or entity type changes - IconCreator combo boxes accumulate duplicate entries when the symbol set changes #63 exactly, and easy to assert on
• defaultSvgFileName, which derives a filename from the symbol
• the amplifier guide's three modes, where switching has to drop the amplifier the previous mode owned

None of that needs a stage or a visible window. jmsfx-core already runs JavaFX-touching tests in the build (IdentificationSymbolIconTest), so the toolkit starts fine under surefire; the same approach would work here.

What it needs

• the junit-bom dependencyManagement entry and the junit-jupiter and hamcrest test dependencies, as jmsfx-core's pom has them
• src/test/java
• a first test over the list rebuilding from IconCreator combo boxes accumulate duplicate entries when the symbol set changes #63, which would have caught it: switch symbol sets several times and assert no list gains duplicates

Not urgent

Nothing here blocks a release, and #63 is fixed and verified without it. Raising it so the gap is recorded rather than rediscovered next time something in the creator misbehaves.