fix(t-paliad-118): /admin/email-templates Verfügbare Variablen — single-column stack

The `.admin-et-variables-list` was a 4-track CSS grid designed for flat
name/type/desc/sample siblings. The renderer wraps each variable in a
`.admin-et-variable-row` div, so each variable became a single grid item —
and 4 rows packed into one visual row, producing the wide multi-column
overflow.

Switch the outer container to `flex-direction: column` (one variable per row)
and the row to a baseline-aligned wrapping flex (name, type pill, desc, sample
left-to-right). `margin-left: auto` pushes the sample right when there's room
and lets it wrap below on narrow widths.

Pre-existing dark-mode issue (`.admin-et-variable-name` hardcoded to #1c1917,
unreadable on dark background) is unchanged by this fix and predates the
layout regression — flagged separately, not in scope here.

frontend/src/styles/global.css

@@ -8233,13 +8233,20 @@ dialog.quick-add-sheet::backdrop {
 }
 
 .admin-et-variables-list {
-    display: grid;
-    grid-template-columns: max-content max-content 1fr max-content;
-    gap: 0.4rem 0.75rem;
+    display: flex;
+    flex-direction: column;
+    gap: 0.4rem;
     margin-top: 0.75rem;
     font-size: 0.85rem;
 }
 
+.admin-et-variable-row {
+    display: flex;
+    align-items: baseline;
+    flex-wrap: wrap;
+    gap: 0.5rem;
+}
+
 .admin-et-variable-name {
     font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
     color: #1c1917;
@@ -8260,6 +8267,7 @@ dialog.quick-add-sheet::backdrop {
 .admin-et-variable-sample {
     color: var(--color-text-muted);
     font-style: italic;
+    margin-left: auto;
     text-align: right;
 }