[FIX] web: Force kanban title opacity in no-content

Before this commit, since there is a mildly transparent filter over the
entire view when the "no content" helper is displayed, the interactive
elements of the empty kanban view (namely: the title with the name and
"quick create" button) were slightly hidden.

This commit enforces a superior z-index on those elements s.t. they can
appear on top of the helper's filter.

closes odoo/odoo#105140

X-original-commit: cbefc9cd51b3c903a6c54d8e3f95bf2b592cf402
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>

addons/web/static/src/views/kanban/kanban_controller.scss

@@ -447,7 +447,7 @@
         }
 
         .oe_kanban_text_red {
-            color: o-text-color('danger');
+            color: o-text-color("danger");
             font-weight: $font-weight-bold;
         }
 
@@ -474,10 +474,12 @@
         .o_kanban_record {
             width: 100%;
         }
-        
+
         @include media-breakpoint-up(md) {
             &.o_kanban_small_column .o_kanban_group:not(.o_column_folded) {
-                flex-basis: calc(var(--KanbanRecord--small-width) + (2 * var(--KanbanGroup-padding-h)));
+                flex-basis: calc(
+                    var(--KanbanRecord--small-width) + (2 * var(--KanbanGroup-padding-h))
+                );
             }
         }
     }
@@ -488,6 +490,9 @@
         padding: 0 var(--KanbanGroup-padding-h) var(--KanbanGroup-padding-bottom);
 
         .o_kanban_header > .o_kanban_header_title {
+            // Makes the title come on top of the "no-content" background gradient.
+            z-index: 2;
+
             &:hover .o_kanban_config,
             .o_kanban_config.show {
                 visibility: visible;