Replace hardcoded 9-symbol registry with dynamic TCBS-based resolution.
Any VN stock ticker is now resolved on first use and cached in KV
permanently. Portfolio flattened from 4 category maps to single assets
map with automatic migration of old format. Crypto, gold, and currency
exchange disabled with "coming soon" message.
Replace hardcoded 0.5% spread with live buy/sell rates from BIDV bank
API. Buying USD uses bank's sell rate (higher), selling USD uses bank's
buy rate (lower). Reply shows both rates and actual spread percentage.
Topup now only accepts VND — users must convert to get other currencies.
Convert uses a 0.5% bid/ask spread: buying USD costs more VND (ask),
selling USD back gives less VND (bid). Simulates real forex behavior.
Paper trading system with 5 commands (trade_topup, trade_buy,
trade_sell, trade_convert, trade_stats). Supports VN stocks via TCBS,
crypto via CoinGecko, forex via ER-API, and gold via PAX Gold proxy.
Per-user portfolio stored in KV with 60s price caching. 54 new tests.
