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/RecipeManager.vue

@@ -91,7 +91,7 @@
     </div>
 
     <!-- Public Recipes Section (admin/senior_editor only) -->
-    <div v-if="auth.isAdmin || auth.user.role === 'senior_editor'" class="recipe-section">
+    <div v-if="auth.canManage" class="recipe-section">
       <h3 class="section-title">🌿 公共配方库 ({{ publicRecipes.length }})</h3>
       <div class="recipe-list">
         <div