Split popup into one file per view

popup/index.js reduced to ~75 lines: loads state, builds a
shared context object, initializes all views, shows first screen.

Each view in popup/views/:
  helpers.js      — $(), showError, hideError, showView
  welcome.js      — welcome screen
  addWallet.js    — unified create/import recovery phrase
  importKey.js    — private key import
  home.js         — wallet list, total value, address derivation
  addressDetail.js — address view, token list, QR, copy
  send.js         — send form, ENS resolution, tx broadcast
  receive.js      — QR + copy
  addToken.js     — token lookup, common token picker
  settings.js     — RPC endpoint
  approval.js     — dApp approval (stub)

Views communicate via a ctx object with shared callbacks
(renderWalletList, showAddressDetail, doRefreshAndRender, etc).

src/popup/views/importKey.js

@@ -0,0 +1,72 @@
+const { $, showError, hideError, showView } = require("./helpers");
+const { addressFromPrivateKey } = require("../../shared/wallet");
+const { encryptWithPassword } = require("../../shared/vault");
+const { state, saveState } = require("../../shared/state");
+
+function show() {
+    $("import-private-key").value = "";
+    $("import-key-password").value = "";
+    $("import-key-password-confirm").value = "";
+    hideError("import-key-error");
+    showView("import-key");
+}
+
+function init(ctx) {
+    $("btn-import-key-confirm").addEventListener("click", async () => {
+        const key = $("import-private-key").value.trim();
+        if (!key) {
+            showError("import-key-error", "Please enter your private key.");
+            return;
+        }
+        let addr;
+        try {
+            addr = addressFromPrivateKey(key);
+        } catch (e) {
+            showError("import-key-error", "Invalid private key.");
+            return;
+        }
+        const pw = $("import-key-password").value;
+        const pw2 = $("import-key-password-confirm").value;
+        if (!pw) {
+            showError("import-key-error", "Please choose a password.");
+            return;
+        }
+        if (pw.length < 8) {
+            showError(
+                "import-key-error",
+                "Password must be at least 8 characters.",
+            );
+            return;
+        }
+        if (pw !== pw2) {
+            showError("import-key-error", "Passwords do not match.");
+            return;
+        }
+        hideError("import-key-error");
+        const encrypted = await encryptWithPassword(key, pw);
+        const walletNum = state.wallets.length + 1;
+        state.wallets.push({
+            type: "key",
+            name: "Wallet " + walletNum,
+            encryptedSecret: encrypted,
+            addresses: [
+                { address: addr, balance: "0.0000", tokenBalances: [] },
+            ],
+        });
+        state.hasWallet = true;
+        await saveState();
+        ctx.renderWalletList();
+        showView("main");
+    });
+
+    $("btn-import-key-back").addEventListener("click", () => {
+        if (!state.hasWallet) {
+            showView("welcome");
+        } else {
+            ctx.renderWalletList();
+            showView("main");
+        }
+    });
+}
+
+module.exports = { init, show };