Grant senior_editor oil editing, PDF export, and public recipe management

Add canManage computed (senior_editor + admin) to auth store and use it
for oil edit/delete buttons, PDF export, and public recipe section
visibility. Backend already allowed these operations for senior_editor.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/OilReference.vue

@@ -118,7 +118,7 @@
           @click="viewMode = 'drop'"
         >滴价</button>
       </div>
-      <button v-if="auth.isAdmin" class="btn-pdf" @click="exportPDF" title="导出PDF">
+      <button v-if="auth.canManage" class="btn-pdf" @click="exportPDF" title="导出PDF">
         📄
       </button>
     </div>
@@ -159,7 +159,7 @@
         <div class="oil-chip-volume" v-if="getMeta(name)?.dropCount">
           {{ volumeLabel(getMeta(name).dropCount) }}
         </div>
-        <div class="oil-actions" v-if="auth.isAdmin" @click.stop>
+        <div class="oil-actions" v-if="auth.canManage" @click.stop>
           <button class="btn-icon-sm" @click="editOil(name)" title="编辑">✏️</button>
           <button class="btn-icon-sm" @click="removeOil(name)" title="删除">🗑️</button>
         </div>