feat(mail) : extract Mail front into Nuxt module layer

LST-67 (2.5) front. Completes the Mail module.

- New frontend/modules/mail/ layer (auto-detected): /mail page (3 columns),
  7 components, mail service + DTO, mail store (folders/messages/unread polling).
- sanitizeMailHtml util and useSystemFolderLabel composable stay global;
  AdminMailTab stays in /admin (service import repointed).
- Consumers repointed: AdminMailTab and PM TaskModal -> ~/modules/mail/...;
  the store is auto-imported (Pinia storesDirs) so the layout badge/polling is
  unchanged.
- /mail gated by the mail module: sidebar.php item with module=mail (so
  SidebarFilter disables /mail when the module is off); the layout filters /mail
  from the API sections to avoid a visual duplicate. ROLE_CLIENT exclusion kept.
- i18n key sidebar.general.mail added.

nuxt build passes; /mail and all other routes preserved.

frontend/modules/mail/pages/mail.vue

@@ -0,0 +1,162 @@
+<script setup lang="ts">
+import type { Task } from '~/modules/project-management/services/dto/task'
+import { useMailStore } from '~/modules/mail/stores/mail'
+
+const { t } = useI18n()
+const router = useRouter()
+const route = useRoute()
+
+useHead({ title: t('mail.title') })
+
+// ─── Store ────────────────────────────────────────────────────────────────
+
+const store = useMailStore()
+const {
+    folderTree,
+    selectedFolderPath,
+    messages,
+    messagesLoading,
+    hasMoreMessages,
+    selectedMessageId,
+    selectedMessageDetail,
+    detailLoading,
+} = storeToRefs(store)
+
+// ─── Init : charge les dossiers + deep-link ───────────────────────────────
+
+onMounted(async () => {
+    if (folderTree.value.length === 0) {
+        await store.fetchFolders()
+    }
+
+    if (!selectedFolderPath.value && folderTree.value.length > 0) {
+        const inbox = folderTree.value.find((f) => f.path.toUpperCase() === 'INBOX')
+        const first = folderTree.value[0]
+        const target = inbox?.path ?? first?.path
+        if (target) {
+            await store.selectFolder(target)
+        }
+    }
+
+    const messageIdParam = route.query.messageId
+    if (messageIdParam) {
+        const id = parseInt(String(messageIdParam), 10)
+        if (!isNaN(id)) {
+            await store.selectMessage(id)
+        }
+    }
+})
+
+// ─── Handlers ─────────────────────────────────────────────────────────────
+
+async function handleFolderSelect(path: string): Promise<void> {
+    await store.selectFolder(path)
+    if (route.query.messageId) {
+        const nextQuery = { ...route.query }
+        delete nextQuery.messageId
+        router.replace({ query: nextQuery })
+    }
+}
+
+async function handleMessageSelect(id: number): Promise<void> {
+    await store.selectMessage(id)
+}
+
+function handleLoadMore(): void {
+    store.fetchMessages(true)
+}
+
+// ─── Modals Phase 6 ────────────────────────────────────────────────────────
+
+const showCreateTaskModal = ref(false)
+const showLinkTaskModal = ref(false)
+const activeMailIdForModal = ref<number | null>(null)
+
+function handleCreateTask(mailId: number): void {
+    activeMailIdForModal.value = mailId
+    showCreateTaskModal.value = true
+}
+
+function handleLinkTask(mailId: number): void {
+    activeMailIdForModal.value = mailId
+    showLinkTaskModal.value = true
+}
+
+function handleTaskCreated(_task: Task): void {
+    showCreateTaskModal.value = false
+    // La tâche est créée et liée côté backend — toast géré par useMailService.createTaskFromMail
+}
+
+function handleTaskLinked(_taskId: number): void {
+    showLinkTaskModal.value = false
+    // Toast géré par useMailService.linkTask
+}
+</script>
+
+<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">
+                {{ t('mail.title') }}
+            </h1>
+            <MailRefreshButton />
+        </div>
+
+        <div class="flex flex-1 overflow-hidden">
+            <aside class="w-[220px] flex-shrink-0 overflow-y-auto border-r border-neutral-200 bg-neutral-50 py-2">
+                <p class="mb-1 px-3 text-xs font-semibold uppercase tracking-wide text-neutral-400">
+                    {{ t('mail.folders') }}
+                </p>
+                <MailFolderTree
+                    :folders="folderTree"
+                    :selected-path="selectedFolderPath"
+                    @select="handleFolderSelect"
+                />
+            </aside>
+
+            <div class="flex w-[320px] flex-shrink-0 flex-col overflow-hidden border-r border-neutral-200 bg-white">
+                <div class="flex flex-shrink-0 items-center justify-between border-b border-neutral-100 px-3 py-2">
+                    <p class="text-xs font-semibold uppercase tracking-wide text-neutral-400">
+                        {{ t('mail.messages') }}
+                    </p>
+                </div>
+                <div class="flex-1 overflow-hidden">
+                    <MailMessageList
+                        :messages="messages"
+                        :selected-id="selectedMessageId"
+                        :loading="messagesLoading"
+                        :has-more="hasMoreMessages"
+                        @select="handleMessageSelect"
+                        @load-more="handleLoadMore"
+                    />
+                </div>
+            </div>
+
+            <div class="flex-1 overflow-hidden bg-white">
+                <MailMessageViewer
+                    :detail="selectedMessageDetail"
+                    :loading="detailLoading"
+                    @create-task="handleCreateTask"
+                    @link-task="handleLinkTask"
+                />
+            </div>
+        </div>
+
+        <!-- Modal créer tâche depuis mail -->
+        <MailCreateTaskModal
+            v-if="activeMailIdForModal !== null"
+            v-model="showCreateTaskModal"
+            :message-id="activeMailIdForModal"
+            :message-detail="selectedMessageDetail"
+            @created="handleTaskCreated"
+        />
+
+        <!-- Modal lier mail à tâche -->
+        <MailLinkTaskModal
+            v-if="activeMailIdForModal !== null"
+            v-model="showLinkTaskModal"
+            :message-id="activeMailIdForModal"
+            @linked="handleTaskLinked"
+        />
+    </div>
+</template>