Fix GDScript ternary and shadowed-identifier warnings in dashboard scripts

Godot's static checker can't unify a float branch with a null branch in
a ternary, so point_value() now uses explicit if/return; renaming the
local sign variable to sign_prefix avoids shadowing the builtin sign().

scripts/ui/dashboard_chart.gd

@@ -99,9 +99,13 @@ func _draw() -> void:
 
 static func point_value(point: Dictionary, series_mode: String) -> Variant:
 	if series_mode == "accuracy":
-		return float(point.get("accuracy", 0)) if int(point.get("total", 0)) > 0 else null
+		if int(point.get("total", 0)) > 0:
+			return float(point.get("accuracy", 0))
+		return null
 	var value: Variant = point.get("questionBankRating", null)
-	return null if value == null else float(value)
+	if value == null:
+		return null
+	return float(value)
 
 
 static func axis_bounds(series_points: Array, series_mode: String) -> Vector2:

scripts/ui/dashboard_screen.gd

@@ -229,8 +229,8 @@ func _render_rating_card(key: String, sparkline: Control, accent: Color, rating_
 	if delta_value != null:
 		var delta := int(delta_value)
 		var arrow := "↗" if delta >= 0 else "↘"
-		var sign := "+" if delta >= 0 else ""
+		var sign_prefix := "+" if delta >= 0 else ""
-		trend_text = "%s %s%d this week" % [arrow, sign, delta]
+		trend_text = "%s %s%d this week" % [arrow, sign_prefix, delta]
 		trend_color = Brand.SUCCESS if delta >= 0 else Brand.MAGENTA
 	if percentile_value != null:
 		caption = "Top %d%% of users" % int(percentile_value)
@@ -269,8 +269,8 @@ func _render_accuracy_card(data: Dictionary) -> void:
 	if delta_value != null:
 		var delta := int(delta_value)
 		var arrow := "↗" if delta >= 0 else "↘"
-		var sign := "+" if delta >= 0 else ""
+		var sign_prefix := "+" if delta >= 0 else ""
-		trend_text = "%s %s%d%% vs last 100" % [arrow, sign, delta]
+		trend_text = "%s %s%d%% vs last 100" % [arrow, sign_prefix, delta]
 		trend_color = Brand.SUCCESS if delta >= 0 else Brand.MAGENTA
 	_set_stat_card("accuracy", "%d%%" % accuracy, trend_text, trend_color, "Last %d questions" % int(data.get("accuracySampleSize", 0)))
 	accuracy_progress_bar.value = accuracy