## Summary
- Adds Binance as a third banking provider alongside EnableBanking and
Indexa Capital
- Binance appears in the institution list for **all countries**, with
the full list sorted alphabetically
- Creates a single "Crypto Portfolio" investment account with total
portfolio value converted to the user's preferred currency
- Supports direct fiat pairs (e.g. BTCEUR), USD stablecoin 1:1 mapping,
and USDT fallback conversion
## Changes
- **Migration**: adds encrypted `api_secret` column to
`banking_connections`
- **BinanceClient**: HMAC-SHA256 authenticated API client for account
data and ticker prices
- **BinanceBalanceSyncService**: converts all non-zero balances to fiat
via direct pairs or USDT fallback
- **BinanceController + ConnectBinanceRequest**: validates credentials,
creates connection and single account
- **SyncBankingConnectionJob**: new `syncBinance()` branch
- **AccountMappingController**: Binance uses Investment account type
- **Frontend**: Binance institution for all countries, API Key + Secret
form fields, alphabetically sorted list
- **Factory**: `binance()` state on `BankingConnectionFactory`
## Test plan
- [x] `BinanceControllerTest` — 6 tests (valid connection, invalid
credentials, account-mapping flag, feature flag, validation, user
currency)
- [x] `BinanceBalanceSyncTest` — 7 tests (direct EUR pair, USDT
fallback, USD stablecoins, locked balances, same-date update, empty
balances, missing external ID)
- [x] Full test suite passes (545 tests)
- [x] Manual: open connection dialog → select any country → Binance
appears alphabetically → select Binance → API Key + Secret form →
connect
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