style(employee) : use MalioSelect built-in label for the phase picker

Replaces the inline <label> with the MalioSelect's native `label` prop
to match the visual style of other selects on the employee detail page.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/pages/employees/[id].vue

@@ -31,8 +31,8 @@
                 </div>
             </div>
             <div v-if="showPicker" class="mt-3 flex items-center gap-3">
-                <label class="text-sm font-bold text-primary-500">Vue contrat</label>
                 <MalioSelect
+                    label="Contrat"
                     :model-value="selectedPhase?.id ?? null"
                     :options="phaseOptions"
                     group-class="w-[420px]"