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/data/exchange_info.cpp

@@ -4,11 +4,19 @@
 
 #include "exchange_info.h"
 
+#include <nlohmann/json.hpp>
+
+#include <algorithm>
+#include <unordered_map>
+
 namespace dragonx {
 namespace data {
 
 const std::vector<ExchangeInfo>& getExchangeRegistry()
 {
+    // Offline seed / fallback. The live list from CoinGecko (parseCoinGeckoTickers)
+    // supersedes this when available; keep the known venues here so the tab is never
+    // empty without network.
     static const std::vector<ExchangeInfo> registry = {
         {
             "Nonkyc.io",
@@ -17,9 +25,68 @@ const std::vector<ExchangeInfo>& getExchangeRegistry()
                 {"DRGX", "USDT", "DRGX/USDT", "https://nonkyc.io/market/DRGX_USDT"},
             }
         },
+        {
+            "OurBit",
+            "https://www.ourbit.com",
+            {
+                {"DRGX", "USDT", "DRGX/USDT", "https://www.ourbit.com/exchange/DRGX_USDT"},
+            }
+        },
     };
     return registry;
 }
 
+namespace {
+// Extract the scheme://host origin from a URL (for ExchangeInfo.baseUrl).
+std::string originOf(const std::string& url)
+{
+    const auto scheme = url.find("://");
+    if (scheme == std::string::npos) return url;
+    const auto host = url.find('/', scheme + 3);
+    return (host == std::string::npos) ? url : url.substr(0, host);
+}
+} // namespace
+
+std::vector<ExchangeInfo> parseCoinGeckoTickers(const std::string& body)
+{
+    std::vector<ExchangeInfo> exchanges;
+    try {
+        const nlohmann::json j = nlohmann::json::parse(body);
+        if (!j.contains("tickers") || !j["tickers"].is_array()) return {};
+
+        std::unordered_map<std::string, size_t> byName;  // exchange name -> index
+        for (const auto& t : j["tickers"]) {
+            if (!t.is_object()) continue;
+            const std::string base   = t.value("base", std::string{});
+            const std::string target = t.value("target", std::string{});
+            std::string market;
+            if (t.contains("market") && t["market"].is_object())
+                market = t["market"].value("name", std::string{});
+            const std::string tradeUrl = t.value("trade_url", std::string{});
+            if (base.empty() || target.empty() || market.empty()) continue;
+
+            auto it = byName.find(market);
+            if (it == byName.end()) {
+                byName[market] = exchanges.size();
+                exchanges.push_back(ExchangeInfo{market, originOf(tradeUrl), {}});
+                it = byName.find(market);
+            }
+            ExchangePair pair{base, target, base + "/" + target, tradeUrl};
+            // Skip duplicate pairs on the same exchange.
+            bool dup = false;
+            for (const auto& p : exchanges[it->second].pairs)
+                if (p.displayName == pair.displayName) { dup = true; break; }
+            if (!dup) exchanges[it->second].pairs.push_back(std::move(pair));
+        }
+    } catch (...) {
+        return {};
+    }
+    // Drop exchanges that ended up with no pairs (defensive).
+    exchanges.erase(std::remove_if(exchanges.begin(), exchanges.end(),
+                    [](const ExchangeInfo& e) { return e.pairs.empty(); }),
+                    exchanges.end());
+    return exchanges;
+}
+
 } // namespace data
 } // namespace dragonx