feat(recipes): restore Copy Recipe Syntax button in recipe modal header

- Add an icon-only copy button next to Send to ComfyUI in the header
  actions row, styled as a textless variant of the neighboring pill
  buttons
- Restore fetchAndCopyRecipeSyntax() wiring against the existing
  /api/lm/recipe/{id}/syntax endpoint (context menu action unaffected)
- Add recipes.actions.copyRecipeSyntax i18n key, reusing the existing
  per-locale translations of the identical context menu string
- Sync modal test fixtures and add copySyntax tests

tests/frontend/components/recipeModal.navigation.test.js

@@ -110,6 +110,7 @@ function recipeModalFixture() {
           </div>
           <div class="recipe-header-actions" id="recipeHeaderActions">
             <button class="modal-send-btn" id="sendRecipeBtn"><i class="fas fa-paper-plane"></i></button>
+            <button class="modal-copy-btn" id="copyRecipeSyntaxBtn"><i class="fas fa-copy"></i></button>
           </div>
           <div id="recipeTagsContainer"></div>
         </header>