Fix Jauge always reading the object's most recent row

A Jauge could only target a whole object, not a specific record —
three gauges pointing at the same "value" field (e.g. Réputation/
Trésorerie/Confiance in one "jauge" object) all silently showed the
most recent row's value, with no way to tell them apart.

Add "Enregistrement (ligne) à suivre" (row_id) so a Jauge targets one
specific row, and "Champ contenant le nom" (champ_nom) to show a
label above the bar — both as dropdowns populated from the object's
actual fields/rows (previously "Champ numérique à afficher" was free
text the user had to type correctly by hand). No regression: without
row_id the widget still falls back to the latest row, exactly as
before.

Extract data_definition_options() (rows+fields for a definition) out
of routes/screens/screen_edit.py so controls_with_values.py can reuse
it server-side for the initial render; a small client-side handler
(bindJaugeDefinitionSelect) repopulates the same selects live when
the tracked object is changed without leaving the panel.

Verified live with Playwright: picking "jauge" then "Confiance" then
"value"/"name" in the panel renders an 80%-filled, green-leaning bar
labelled "Confiance" on /play — not the 20%/50% of the other rows.

screens/__init__.py

@@ -43,6 +43,7 @@ from .widgets.layout_capable_widgets import LAYOUT_CAPABLE_WIDGETS
 from .widgets.font_options import GOOGLE_FONTS_LINK
 from .widgets.widget_meta import widget_meta
 from .widgets.controls_with_values import controls_with_values
+from .widgets.data_definition_options import data_definition_options
 
 from .labels.trigger_labels import TRIGGER_LABELS
 from .labels.action_type_labels import ACTION_TYPE_LABELS