Replace old 150-token list with 511-token tokenList.js

Delete src/shared/tokens.js and migrate all consumers to
src/shared/tokenList.js which has 511 tokens (vs ~150) sourced
from CoinGecko with on-chain verified decimals.

- prices.js: getTopTokenPrices now from tokenList
- transactions.js: KNOWN_SYMBOLS now from tokenList (3.4x more
  symbols for spoof detection)
- send.js: KNOWN_SYMBOLS for token dropdown filtering
- approval.js: uses pre-built TOKEN_BY_ADDRESS map instead of
  constructing its own from TOKENS array
- addToken.js: uses getTopTokens(25) for quick-pick buttons
  (only top 25 shown, not all 511)

src/shared/tokenList.js

@@ -5,6 +5,10 @@
 //
 // 511 tokens.
 
+const { debugFetch } = require("./log");
+
+const COINDESK_API = "https://data-api.coindesk.com/index/cc/v1/latest/tick";
+
 const TOKENS = [
     {
         address: "0xdAC17F958D2ee523a2206206994597C13D831ec7",
@@ -2585,4 +2589,37 @@ for (const t of TOKENS) {
     }
 }
 
-module.exports = { TOKENS, TOKEN_BY_ADDRESS, KNOWN_SYMBOLS, getTopTokens };
+// Fetch USD prices for the top N tokens from CoinDesk.
+// Also always includes ETH. Returns { ETH: 1234.56, LINK: 8.60, ... }.
+// n must be <= 30 (API and sanity limit).
+async function getTopTokenPrices(n) {
+    if (n > 30) {
+        throw new Error("getTopTokenPrices: n must be <= 30, got " + n);
+    }
+    const symbols = ["ETH", ...TOKENS.slice(0, n).map((t) => t.symbol)];
+    const unique = [...new Set(symbols)];
+    const instruments = unique.map((s) => s + "-USD").join(",");
+    const url =
+        COINDESK_API +
+        "?market=cadli&instruments=" +
+        instruments +
+        "&apply_mapping=true";
+    const resp = await debugFetch(url);
+    const json = await resp.json();
+    const prices = {};
+    for (const [instrument, data] of Object.entries(json.Data || {})) {
+        const symbol = instrument.split("-")[0];
+        if (data.VALUE !== undefined) {
+            prices[symbol] = data.VALUE;
+        }
+    }
+    return prices;
+}
+
+module.exports = {
+    TOKENS,
+    TOKEN_BY_ADDRESS,
+    KNOWN_SYMBOLS,
+    getTopTokens,
+    getTopTokenPrices,
+};