Persist navigation state across popup close/reopen

The current view, selected wallet, selected address, and selected
token are now saved to extension storage. When the popup reopens,
it restores to the last visited view instead of always returning
to the home screen.

Restorable views: main, address detail, address-token, receive,
settings. Non-restorable views (send, confirm, tx status, forms)
fall back to the nearest parent. Stored indices are validated
against current wallet data to handle stale references.

Also refactors receive view setup into a centralized receive.show()
function, eliminating duplicate QR/address/warning code from
addressDetail.js, addressToken.js, and home.js. Adds settings.show()
to centralize settings field population.

src/popup/index.js

@@ -52,8 +52,67 @@ const ctx = {
     showAddressToken: () => addressToken.show(),
     showAddTokenView: () => addToken.show(),
     showConfirmTx: (txInfo) => confirmTx.show(txInfo),
+    showReceive: () => receive.show(),
 };
 
+// Views that can be fully re-rendered from persisted state.
+// All others fall back to the nearest restorable parent.
+const RESTORABLE_VIEWS = new Set([
+    "main",
+    "address",
+    "address-token",
+    "receive",
+    "settings",
+]);
+
+function restoreView() {
+    const view = state.currentView;
+    if (!view || !RESTORABLE_VIEWS.has(view)) {
+        return fallbackView();
+    }
+
+    // Validate that selectedWallet/selectedAddress still point to valid data
+    if (view === "address" || view === "address-token" || view === "receive") {
+        if (
+            state.selectedWallet === null ||
+            state.selectedAddress === null ||
+            !state.wallets[state.selectedWallet] ||
+            !state.wallets[state.selectedWallet].addresses[
+                state.selectedAddress
+            ]
+        ) {
+            return fallbackView();
+        }
+    }
+
+    if (view === "address-token" && !state.selectedToken) {
+        return fallbackView();
+    }
+
+    switch (view) {
+        case "address":
+            addressDetail.show();
+            break;
+        case "address-token":
+            addressToken.show();
+            break;
+        case "receive":
+            receive.show();
+            break;
+        case "settings":
+            settings.show();
+            break;
+        default:
+            fallbackView();
+            break;
+    }
+}
+
+function fallbackView() {
+    renderWalletList();
+    showView("main");
+}
+
 async function init() {
     if (DEBUG) {
         const banner = document.createElement("div");
@@ -98,10 +157,7 @@ async function init() {
             showView("main");
             return;
         }
-        $("settings-rpc").value = state.rpcUrl;
-        $("settings-blockscout").value = state.blockscoutUrl;
-        settings.renderSiteLists();
-        showView("settings");
+        settings.show();
     });
 
     welcome.init(ctx);
@@ -121,7 +177,7 @@ async function init() {
         showView("welcome");
     } else {
         renderWalletList();
-        showView("main");
+        restoreView();
         doRefreshAndRender();
         setInterval(doRefreshAndRender, 10000);
     }