feat(market): auto-populate exchange pairs from CoinGecko (adds OurBit); DRGX dashboard

- Fetch /coins/dragonx-2/tickers once per session (App::refreshExchanges, reusing the
  price-fetch worker path) and build the exchange registry at runtime into
  state.market.exchanges; parseCoinGeckoTickers groups tickers by venue. The Market tab
  sources from this live list and falls back to the compiled-in registry (now including
  OurBit + Nonkyc.io) when offline. Fixes the missing OurBit pair and auto-tracks future
  listings.
- Fix stale selection defaults (TradeOgre / DRGX-BTC -> Nonkyc.io / DRGX/USDT) that never
  matched the registry, and make the attribution generic ("Price data from CoinGecko").
- Reframe the single-asset portfolio card as a DRGX holdings dashboard: relabel to
  "MY DRGX" and show the 24h change on the holdings value (colored by direction).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/util/i18n.cpp

@@ -1052,13 +1052,14 @@ void I18n::loadBuiltinEnglish()
         strings_["market_24h"] = "24h";
         strings_["market_24h_volume"] = "24H VOLUME";
         strings_["market_6h"] = "6h";
-        strings_["market_attribution"] = "Price data from NonKYC";
+        strings_["market_attribution"] = "Price data from CoinGecko";
         strings_["market_btc_price"] = "BTC PRICE";
         strings_["market_no_history"] = "No price history available";
         strings_["market_no_price"] = "No price data";
         strings_["market_now"] = "Now";
         strings_["market_pct_shielded"] = "%.0f%% Shielded";
-        strings_["market_portfolio"] = "PORTFOLIO";
+        strings_["market_portfolio"] = "MY DRGX";
+        strings_["market_24h_change"] = "24h";
         strings_["market_price_loading"] = "Loading price data...";
         strings_["market_price_unavailable"] = "Price data unavailable";
         strings_["market_refresh_price"] = "Refresh price data";