fix: read USD prices from Chainlink price feeds through the RPC endpoint (closes #525)

CoinDesk now refuses requests without an API key, so mainnet showed no USD prices. Mainnet prices now come from Chainlink's USD price feeds, read with eth_call through the user's RPC endpoint; no other service is asked. The bundled list pairs each of 53 tokens with its feed by contract address, and ETH and WETH use ETH/USD. The popup reads the feeds of ETH and the tokens the user holds or tracks in one batched request, at most every 5 minutes. A reading older than its heartbeat plus 30 minutes, or not positive, is no price. A token with no feed shows no USD value. CoinDesk is gone.

RULES.md still names the CoinDesk price API.

Model: opus-5-5

src/popup/views/helpers.js

@@ -439,7 +439,7 @@ function balanceLinesForAddress(addr, trackedTokens, showZero) {
         html += balanceLine(
             t.symbol,
             bal,
-            getPrice(t.symbol),
+            getPrice(t.address),
             t.address.toLowerCase(),
         );
         seen.add(t.address.toLowerCase());
@@ -450,7 +450,7 @@ function balanceLinesForAddress(addr, trackedTokens, showZero) {
             html += balanceLine(
                 t.symbol,
                 0,
-                getPrice(t.symbol),
+                getPrice(t.address),
                 t.address.toLowerCase(),
             );
         }