feat : add admin page for task configuration

Add admin page with tabs for managing task statuses, efforts,
priorities and types, with CRUD drawers and color picker.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/pages/admin.vue

@@ -0,0 +1,45 @@
+<template>
+    <div>
+        <h1 class="text-2xl font-bold text-neutral-900">Administration</h1>
+
+        <div class="mt-6 border-b border-neutral-200">
+            <nav class="flex gap-6">
+                <button
+                    v-for="tab in tabs"
+                    :key="tab.key"
+                    class="px-1 pb-3 text-sm font-semibold transition"
+                    :class="activeTab === tab.key
+                        ? 'border-b-2 border-primary-500 text-primary-500'
+                        : 'text-neutral-500 hover:text-neutral-700'"
+                    @click="activeTab = tab.key"
+                >
+                    {{ tab.label }}
+                </button>
+            </nav>
+        </div>
+
+        <div class="mt-6">
+            <AdminStatusTab v-if="activeTab === 'statuses'" />
+            <AdminEffortTab v-if="activeTab === 'efforts'" />
+            <AdminPriorityTab v-if="activeTab === 'priorities'" />
+            <AdminTypeTab v-if="activeTab === 'types'" />
+            <AdminUserTab v-if="activeTab === 'users'" />
+        </div>
+    </div>
+</template>
+
+<script setup lang="ts">
+useHead({ title: 'Administration' })
+
+const tabs = [
+    { key: 'statuses', label: 'Statuts' },
+    { key: 'efforts', label: 'Efforts' },
+    { key: 'priorities', label: 'Priorités' },
+    { key: 'types', label: 'Types' },
+    { key: 'users', label: 'Utilisateurs' },
+] as const
+
+type TabKey = typeof tabs[number]['key']
+
+const activeTab = ref<TabKey>('statuses')
+</script>