Every tr() source string in the code and the forms is now the English
text, and French is a translation (qet_fr.ts) like the other languages.
Generated, not hand-edited: master ef795a21e5 converted by
qet-en-source (harness 4c4ddc9).
3144 messages get an English source, 665 already had one, 0 left French; 8 shared-wording pairs disambiguated.
C++: 2904 literals in 233 files. Forms: 809 strings in 65 files. All 34 .ts files re-keyed; qet_fr.ts filled.
lupdate check: PASS. What each of 38 languages shows, old vs new: same 118266, English instead of French 38433, comment fallback 51, differences 0.
ElementInfoWidget's fixed ~40 predefined ELMT_* keys had no way for a
user to add a genuinely new element-info key, even though DiagramContext
already stores/round-trips arbitrary keys generically via toXml()/fromXml().
Adds an "Ajouter une propriété personnalisée" button that appends a
CustomElementInfoPartWidget row (both key and value user-editable,
unlike the fixed ElementInfoPartWidget rows bound to one predefined
key). The typed key is validated live against the existing
DiagramContext::isKeyAcceptable() and flagged with a red border when
it doesn't match, instead of silently dropping it. Any key already
present on the element that isn't one of the predefined/special keys
is re-displayed as a custom row on next selection.
Implements the scope proposed in discussion #611.