feat: expand confirm-tx warnings — closes #114 (#118)

Expands the confirm-tx warning system with three new warning types, all using the existing `visibility:hidden/visible` pattern from PR #98 (no animations, no layout shift).

## Changes

1. **Scam address list expanded** (7 → 652 addresses): Sourced from [MyEtherWallet/ethereum-lists](https://github.com/MyEtherWallet/ethereum-lists) darklist (MIT license). Checked synchronously before sending.

2. **Contract address warning**: When the recipient is a smart contract (detected via `getCode`), shows a warning that sending directly to a contract may result in permanent loss of funds.

3. **Null/burn address warning**: Detects known burn addresses (`0x0000...0000`, `0x...dead`, `0x...deadbeef`) and warns that funds are permanently destroyed.

4. **No-history warning** (existing from #98): Unchanged, still shows for EOAs with zero transaction history.

All warnings use reserved-space `visibility:hidden/visible` elements — no layout shift, no animations.

closes #114

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: clawbot <clawbot@eeqj.de>
Reviewed-on: #118
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>
Co-committed-by: clawbot <sneak+clawbot@sneak.cloud>

src/background/index.js

@@ -12,6 +12,11 @@ const { refreshBalances, getProvider } = require("../shared/balances");
 const { debugFetch } = require("../shared/log");
 const { decryptWithPassword } = require("../shared/vault");
 const { getSignerForAddress } = require("../shared/wallet");
+const {
+    isPhishingDomain,
+    updatePhishingList,
+    startPeriodicRefresh,
+} = require("../shared/phishingDomains");
 
 const storageApi =
     typeof browser !== "undefined"
@@ -571,6 +576,11 @@ async function backgroundRefresh() {
 
 setInterval(backgroundRefresh, BACKGROUND_REFRESH_INTERVAL);
 
+// Fetch the phishing domain blocklist delta on startup and refresh every 24h.
+// The vendored blocklist is bundled at build time; this fetches only new entries.
+updatePhishingList();
+startPeriodicRefresh();
+
 // When approval window is closed without a response, treat as rejection
 if (windowsApi && windowsApi.onRemoved) {
     windowsApi.onRemoved.addListener((windowId) => {
@@ -643,6 +653,8 @@ runtime.onMessage.addListener((msg, sender, sendResponse) => {
                 resp.type = "sign";
                 resp.signParams = approval.signParams;
             }
+            // Flag if the requesting domain is on the phishing blocklist.
+            resp.isPhishingDomain = isPhishingDomain(approval.hostname);
             sendResponse(resp);
         } else {
             sendResponse(null);