feat: add a Crypto tab with live CoinGecko prices synced into Net Worth

Track individual coins (identity + quantity) in a dedicated tab, backed by
CoinGecko's Demo API (AURUM_COINGECKO_API_KEY). A holding is just another
Asset under the hood (asset_class=crypto) with its value written as a
regular AssetValuation — the existing Net Worth aggregation needs zero
changes to pick it up.

Prices never refresh in the background (no scheduler in this stack, same
reasoning as recurring transactions): a "Refresh prices" button forces a
sync, and GET /crypto/holdings lazily re-syncs at most once every 24h.
CoinGecko outages leave existing values untouched (error_key: "unreachable")
instead of failing the request. Backup/restore now carries CryptoHolding
rows too, so a restore doesn't silently strip a holding's coin identity.

Backend: 75/75 tests passing (9 new), including a real identity-map
staleness bug the tests caught in the raw-Core-upsert + ORM re-read pattern,
fixed via populate_existing=True.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01855PiW5Wd8n4aRW4n9kByY

frontend/src/lib/i18n.ts

@@ -7,6 +7,7 @@ const STORAGE_KEY = "aurum:language";
 const ru = {
   "nav.dashboard": "Дашборд",
   "nav.netWorth": "Капитал",
+  "nav.crypto": "Криптовалюта",
   "nav.roi": "Доходность",
   "nav.transactions": "Транзакции",
   "nav.accounts": "Счета",
@@ -107,6 +108,25 @@ const ru = {
   "netWorth.assetsTable.asOf": "на {{date}}",
   "netWorth.assetsTable.annualRoi": "{{percent}}% годовых",
 
+  "crypto.addButton": "Добавить монету",
+  "crypto.refreshButton": "Обновить цены",
+  "crypto.refreshing": "Обновление…",
+  "crypto.lastSynced": "Обновлено {{time}}",
+  "crypto.neverSynced": "Цены ещё не загружались",
+  "crypto.totalValueLabel": "Всего в криптовалюте",
+  "crypto.empty": "Пока нет ни одной монеты. Добавьте первую, чтобы начать отслеживать.",
+  "crypto.pendingPrice": "цена ещё не получена",
+  "crypto.confirmDelete": "Убрать «{{name}}» из отслеживания?",
+  "crypto.syncError.unreachable": "Не удалось подключиться к CoinGecko — показаны последние известные цены.",
+  "crypto.search.placeholder": "Найти монету (например, Bitcoin или BTC)…",
+  "crypto.search.hint": "Начните вводить название или тикер монеты.",
+  "crypto.search.empty": "Ничего не найдено.",
+  "crypto.search.noApiKey": "Не настроен ключ CoinGecko API — задайте AURUM_COINGECKO_API_KEY в .env (бесплатный ключ на coingecko.com/en/api/pricing).",
+  "crypto.form.quantityLabel": "Количество",
+  "crypto.form.addTitle": "Добавить {{name}}",
+  "crypto.form.editTitle": "Изменить количество: {{name}}",
+  "crypto.form.saveError": "Не удалось сохранить. Проверьте данные и попробуйте снова.",
+
   "roi.calculator.title": "Калькулятор ROI",
   "roi.calculator.investmentLabel": "Сумма инвестиции",
   "roi.calculator.monthlyIncomeLabel": "Доход в месяц",
@@ -415,6 +435,7 @@ const ru = {
 const en: Record<keyof typeof ru, string> = {
   "nav.dashboard": "Dashboard",
   "nav.netWorth": "Net Worth",
+  "nav.crypto": "Crypto",
   "nav.roi": "Returns",
   "nav.transactions": "Transactions",
   "nav.accounts": "Accounts",
@@ -515,6 +536,25 @@ const en: Record<keyof typeof ru, string> = {
   "netWorth.assetsTable.asOf": "as of {{date}}",
   "netWorth.assetsTable.annualRoi": "{{percent}}%/year",
 
+  "crypto.addButton": "Add coin",
+  "crypto.refreshButton": "Refresh prices",
+  "crypto.refreshing": "Refreshing…",
+  "crypto.lastSynced": "Updated {{time}}",
+  "crypto.neverSynced": "Prices haven't loaded yet",
+  "crypto.totalValueLabel": "Total in crypto",
+  "crypto.empty": "No coins yet. Add your first one to start tracking.",
+  "crypto.pendingPrice": "price not fetched yet",
+  "crypto.confirmDelete": "Remove \"{{name}}\" from tracking?",
+  "crypto.syncError.unreachable": "Could not reach CoinGecko — showing the last known prices.",
+  "crypto.search.placeholder": "Find a coin (e.g. Bitcoin or BTC)…",
+  "crypto.search.hint": "Start typing a coin's name or ticker.",
+  "crypto.search.empty": "Nothing found.",
+  "crypto.search.noApiKey": "CoinGecko API key not configured — set AURUM_COINGECKO_API_KEY in .env (free key at coingecko.com/en/api/pricing).",
+  "crypto.form.quantityLabel": "Quantity",
+  "crypto.form.addTitle": "Add {{name}}",
+  "crypto.form.editTitle": "Edit quantity: {{name}}",
+  "crypto.form.saveError": "Failed to save. Check the data and try again.",
+
   "roi.calculator.title": "ROI Calculator",
   "roi.calculator.investmentLabel": "Investment amount",
   "roi.calculator.monthlyIncomeLabel": "Monthly income",