fix: resolve token symbols from multiple sources (closes #51)

When tokenBalances doesn't contain an entry for a token (e.g. before
balances are fetched), the symbol fell back to '?' in addressToken
and send views.

Add resolveSymbol() helper that checks tokenBalances → TOKEN_BY_ADDRESS
(known tokens) → trackedTokens → truncated address as last resort.

Fixes USDC and other known tokens showing '?' when balance data
hasn't loaded yet.

src/popup/views/addressToken.js

@@ -12,7 +12,7 @@ const {
     balanceLine,
 } = require("./helpers");
 const { state, currentAddress, saveState } = require("../../shared/state");
-const { TOKEN_BY_ADDRESS } = require("../../shared/tokenList");
+const { TOKEN_BY_ADDRESS, resolveSymbol } = require("../../shared/tokenList");
 const {
     formatUsd,
     getPrice,
@@ -96,14 +96,11 @@ function show() {
         const tb = (addr.tokenBalances || []).find(
             (t) => t.address.toLowerCase() === tokenId.toLowerCase(),
         );
-        const tracked = (state.trackedTokens || []).find(
-            (t) => t.address.toLowerCase() === tokenId.toLowerCase(),
+        symbol = resolveSymbol(
+            tokenId,
+            addr.tokenBalances,
+            state.trackedTokens,
         );
-        symbol =
-            (tb && tb.symbol) ||
-            (tracked && tracked.symbol) ||
-            (knownToken && knownToken.symbol) ||
-            "?";
         amount = tb ? parseFloat(tb.balance || "0") : 0;
         price = getPrice(symbol);
     }