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/views/OilReference.vue

@@ -247,7 +247,7 @@ const recipesWithOil = computed(() => {
 })
 
 function getMeta(name) {
-  return oils.oilsMeta.get(name)
+  return oils.oilsMeta[name]
 }
 
 function getDropsForOil(recipe, oilName) {
@@ -280,7 +280,7 @@ async function addOil() {
 
 function editOil(name) {
   editingOilName.value = name
-  const meta = oils.oilsMeta.get(name)
+  const meta = oils.oilsMeta[name]
   editBottlePrice.value = meta?.bottlePrice || 0
   editDropCount.value = meta?.dropCount || 0
   editRetailPrice.value = meta?.retailPrice || null