refactor(ui): tabs align with default sidenav offset + tighten gap below tabs

- CoreSurfaceTabBar: add `mx-4` to `<v-tabs>` so the tab strip aligns
  horizontally with PageHeader's title icon (both now use the same 16px
  inset inside `v-container fluid`).
- user.view.vue + admin.layout.vue: add `pb-0` on the parent
  `<v-container fluid>` to collapse ~16px of dead space between the tab
  underline and the routed child's top edge. Child views own their own
  top padding via their own `<v-container fluid>` + `pa-2` row.

Visual impact (Account, Org detail, Admin surfaces):
- Tabs now align with the section title icon instead of being 16px to the left
- Vertical gap below tabs drops from ~40px to ~24px

Author: PierreBrisorgueil

src/modules/admin/views/admin.layout.vue

@@ -1,5 +1,5 @@
 <template>
-  <v-container fluid>
+  <v-container fluid class="pb-0">
     <v-alert
       v-if="error"
       type="error"

src/modules/core/components/core.surfaceTabBar.component.vue

@@ -54,7 +54,7 @@ function tabTo(route) {
 </script>
 
 <template>
-  <v-tabs>
+  <v-tabs class="mx-4">
     <v-tab
       v-for="t in visibleTabs"
       :key="t.value"

src/modules/users/views/user.view.vue

@@ -1,7 +1,8 @@
 <template>
   <div>
-    <!-- Layout chrome: header + tab bar, guttered with their own container -->
-    <v-container fluid>
+    <!-- Layout chrome: header + tab bar, guttered with their own container.
+         pb-0 collapses the gap below tabs — child router-view supplies its own top padding. -->
+    <v-container fluid class="pb-0">
       <PageHeader icon="fa-solid fa-user" title="Account">
         <template #actions>
           <organizationsSwitcherComponent />