The charging tabs drag, like a car's do

Reordering the bar meant editing the template, which is a poor way to ask for
Home chargers first. The tabs now drag into either order on the same native
drag events as a car's tabs and the garage, down to the live reorder as the
pointer crosses a tab, the grab cursor, and the rail's lock holding the bar
still for anyone who would rather not nudge it on the way to a tab.

The arrangement is saved on the profile as charger_tab_order, beside the garage
order and for the same reason: it is a layout choice that should follow the
account rather than the browser, unlike which cards are folded. The field is
reconciled onto the users collection at boot, so no migration step. Its
normalizer is the garage's, which now takes the field name and cap as
arguments instead of being copied.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

API Server/internal/models/models.go

@@ -495,7 +495,8 @@ type User struct {
 	// CarOrder is the garage arrangement: car ids in the order this user dragged
 	// them into. The car list is already returned in this order, so a client only
 	// needs it to send an updated arrangement back.
-	CarOrder []string `json:"carOrder"`
+	CarOrder        []string `json:"carOrder"`
+	ChargerTabOrder []string `json:"chargerTabOrder"`
 
 	// Non-empty while an account-deletion request is pending its cooldown.
 	DeletionRequestedAt *time.Time `json:"deletionRequestedAt,omitempty"`