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

locales/ja.json

@@ -860,6 +860,7 @@
         "actions": {
             "sendCheckpoint": "ComfyUIへ送信",
             "sendRecipe": "ComfyUIへ送信",
+            "copyRecipeSyntax": "レシピ構文をコピー",
             "deleteRecipeWithShortcut": "レシピを削除（Del）"
         },
         "navigation": {