style(front) : ajuste l'espacement sous les titres + PageHeader sur la messagerie

- Retire les marges hautes redondantes (doublon avec le pb du PageHeader) :
  dashboard (KPI), my-tasks (kanban + liste), time-tracking, documents
- Messagerie : titre passé sur <PageHeader> (cohérent avec les autres pages),
  bouton refresh déplacé dans #actions

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/modules/mail/pages/mail.vue

@@ -95,11 +95,13 @@ function handleTaskLinked(_taskId: number): void {
 
 <template>
     <div class="flex h-full flex-col overflow-hidden">
-        <div class="flex flex-shrink-0 items-center justify-between border-b border-neutral-200 bg-white px-4 py-3">
-            <h1 class="text-lg font-semibold text-neutral-900">
+        <div class="flex-shrink-0">
+            <PageHeader>
                 {{ t('mail.title') }}
-            </h1>
-            <MailRefreshButton />
+                <template #actions>
+                    <MailRefreshButton />
+                </template>
+            </PageHeader>
         </div>
 
         <div class="flex flex-1 overflow-hidden">

frontend/modules/project-management/pages/my-tasks.vue

@@ -450,7 +450,7 @@ onMounted(async () => {
 
         <!-- Kanban View — grouped by canonical category -->
         <div v-if="viewMode === 'kanban'">
-            <div class="mt-6 flex h-[calc(100vh-260px)] gap-3 overflow-x-auto pb-4">
+            <div class="flex h-[calc(100vh-260px)] gap-3 overflow-x-auto pb-4">
                 <div
                     v-for="cat in CATEGORIES"
                     :key="cat"
@@ -510,7 +510,7 @@ onMounted(async () => {
         </div>
 
         <!-- List View -->
-        <div v-if="viewMode === 'list'" class="mt-6 flex flex-col gap-2.5 rounded-[10px] bg-tertiary-500 p-2.5">
+        <div v-if="viewMode === 'list'" class="flex flex-col gap-2.5 rounded-[10px] bg-tertiary-500 p-2.5">
             <TaskBulkActions
                 :selected-count="selectedTaskIds.size"
                 :total-count="tasks.length"

frontend/modules/time-tracking/pages/time-tracking.vue

@@ -98,7 +98,7 @@
             </PageHeader>
         </div>
 
-        <div class="relative z-0 mt-4 -mb-24 min-h-0 flex-1">
+        <div class="relative z-0 -mb-24 min-h-0 flex-1">
             <TimeEntryList
                 v-if="viewMode === 'list'"
                 :entries="filteredEntries"

frontend/pages/documents.vue

@@ -12,7 +12,7 @@
         </nav>
 
         <!-- Filtre local + rechargement -->
-        <div class="mt-4 flex items-center gap-2">
+        <div class="flex items-center gap-2">
             <div class="max-w-sm flex-1">
                 <MalioInputText
                     v-model="filter"

frontend/pages/index.vue

@@ -548,7 +548,7 @@ const lineOptions = {
 
         <template v-else>
             <!-- KPI Cards -->
-            <div class="mt-6 grid grid-cols-2 gap-4 lg:grid-cols-4">
+            <div class="grid grid-cols-2 gap-4 lg:grid-cols-4">
                 <div class="rounded-xl border border-neutral-100 bg-neutral-50 p-5">
                     <p class="text-xs font-medium uppercase tracking-wider text-neutral-400">
                         {{ $t('dashboard.stats.hoursPeriod') }}