Fix critical bugs: oil prices ¥0.00, ingredient field mapping

- oils store: change Map to plain object for Vue reactivity
- recipes store: map `oil_name` from API (was only mapping `oil`/`name`)
- OilReference: fix .get() calls to bracket access
- Add price-display.cy.js regression test (3 tests)
- Add visual-check.cy.js for screenshot verification

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

frontend/src/stores/recipes.js

@@ -19,7 +19,7 @@ export const useRecipesStore = defineStore('recipes', () => {
       note: r.note ?? '',
       tags: r.tags ?? [],
       ingredients: (r.ingredients ?? []).map((ing) => ({
-        oil: ing.oil ?? ing.name,
+        oil: ing.oil_name ?? ing.oil ?? ing.name,
         drops: ing.drops,
       })),
     }))