Token auto-discovery, tx history, balance polling, EIP-6963, UI overhaul

Major changes:
- Fetch token balances and tx history from Blockscout API (configurable)
- Remove manual token discovery (discoverTokens) in favor of Blockscout
- HD address gap scanning on mnemonic import
- Duplicate mnemonic detection on wallet add
- EIP-6963 multi-wallet discovery + selectedAddress updates in inpage
- Two-tier balance refresh: 10s while popup open, 60s background
- Fix $0.00 flash before prices load (return null when no prices)
- No-layout-shift: min-height on total value element
- Aligned balance columns (42ch address width, consistent USD column)
- All errors use flash messages instead of off-screen error divs
- Settings gear in global title bar, add-wallet moved to settings pane
- Settings wells with light grey background, configurable Blockscout URL
- Consistent "< Back" buttons top-left on all views
- Address titles (Address 1.1, 1.2, etc.) on main and detail views
- Send view shows current balance of selected asset
- Clickable affordance policy added to README
- Shortened mnemonic backup warning
- Fix broken background script constant imports

src/popup/index.js

@@ -1,11 +1,11 @@
 // AutistMask popup entry point.
 // Loads state, initializes views, triggers first render.
 
-const { DEBUG } = require("../shared/wallet");
+const { DEBUG } = require("../shared/constants");
 const { state, saveState, loadState } = require("../shared/state");
 const { refreshPrices } = require("../shared/prices");
 const { refreshBalances } = require("../shared/balances");
-const { showView } = require("./views/helpers");
+const { $, showView } = require("./views/helpers");
 
 const home = require("./views/home");
 const welcome = require("./views/welcome");
@@ -23,13 +23,22 @@ function renderWalletList() {
     home.render(ctx);
 }
 
+let refreshInFlight = false;
+
 async function doRefreshAndRender() {
-    await Promise.all([
-        refreshPrices(),
-        refreshBalances(state.wallets, state.trackedTokens, state.rpcUrl),
-    ]);
-    await saveState();
-    renderWalletList();
+    if (refreshInFlight) return;
+    refreshInFlight = true;
+    try {
+        await Promise.all([
+            refreshPrices(),
+            refreshBalances(state.wallets, state.rpcUrl, state.blockscoutUrl),
+        ]);
+        state.lastBalanceRefresh = Date.now();
+        await saveState();
+        renderWalletList();
+    } finally {
+        refreshInFlight = false;
+    }
 }
 
 const ctx = {
@@ -54,6 +63,12 @@ async function init() {
 
     await loadState();
 
+    $("btn-settings").addEventListener("click", () => {
+        $("settings-rpc").value = state.rpcUrl;
+        $("settings-blockscout").value = state.blockscoutUrl;
+        showView("settings");
+    });
+
     welcome.init(ctx);
     addWallet.init(ctx);
     importKey.init(ctx);
@@ -72,6 +87,7 @@ async function init() {
         renderWalletList();
         showView("main");
         doRefreshAndRender();
+        setInterval(doRefreshAndRender, 10000);
     }
 }