feat(market): per-exchange price chart from each venue's own candle API

The market chart was hardwired to CoinGecko's cross-exchange USD aggregate
(vs_currency=usd), so selecting a trading pair only changed the "Trade" link —
never the chart or price. Now the SELECTED exchange drives both.

CoinGecko gives us which venues list DRGX (the ticker `market.identifier`) but
not their APIs, so add data/exchange_candles.h: a hand-maintained map from that
identifier to each venue's public candle endpoint, with two adapters verified
against the live APIs — Ourbit (MEXC-style /api/v3/klines, array format) and
NonKYC (TradingView-UDF /market/candles, `bars`). Unmapped venues return no URL,
so the chart falls back to the CoinGecko aggregate and nothing regresses.

- App::refreshExchangeChart() resolves the selected pair, fetches its intraday
  (5-min) + daily candles via the TLS-verified httpGetString on the worker, and
  stores them on MarketInfo (exchange_chart_intraday/daily + exchange_chart_active).
  Re-fetches on pair change; self-throttled to ~30 min otherwise; falls back to
  aggregate on any failure.
- chartSeries() draws the per-exchange series when active (portfolio sparklines
  stay on the aggregate). The hero shows the selected venue's real price
  (converted_last) — Ourbit vs NonKYC differ ~7%. parseCoinGeckoTickers now
  captures the identifier + per-exchange USD price (previously discarded).

Adapters unit-tested against real captured responses (URL builder + both parsers
+ the chartSeries switch) and validated against the full live feeds (Ourbit 20d,
NonKYC 370d, ascending, correct closes). Build + ctest + hygiene green.

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

src/data/wallet_state.h

@@ -175,6 +175,14 @@ struct MarketInfo {
     std::chrono::steady_clock::time_point chart_last_fetch_time{};
     bool chart_loaded = false;
 
+    // Per-EXCHANGE candle series for the SELECTED pair, fetched from that venue's own API (see
+    // data/exchange_candles.h). When exchange_chart_active is true the Market chart draws these instead
+    // of the CoinGecko cross-exchange aggregate above; it's set false while switching pairs or when the
+    // selected venue has no adapter / its fetch failed, so the chart gracefully falls back to aggregate.
+    std::vector<std::pair<std::time_t, double>> exchange_chart_intraday;
+    std::vector<std::pair<std::time_t, double>> exchange_chart_daily;
+    bool exchange_chart_active = false;
+
     // Exchanges/pairs fetched live from CoinGecko (empty until fetched; the Market tab
     // falls back to data::getExchangeRegistry() while empty).
     std::vector<data::ExchangeInfo> exchanges;