feat: expand confirm-tx warnings — closes #114

- Refactor address warnings into src/shared/addressWarnings.js module
  - getLocalWarnings(address, options): sync checks against local lists
  - getFullWarnings(address, provider, options): async local + RPC checks
- Expand scam address list from 652 to 2417 addresses
  - Added EtherScamDB (MIT) as additional source
- Update confirmTx.js to use the new addressWarnings module

src/popup/index.html

@@ -605,6 +605,31 @@
                         Double-check the address before sending.
                     </div>
                 </div>
+                <div
+                    id="confirm-contract-warning"
+                    class="mb-2"
+                    style="visibility: hidden"
+                >
+                    <div
+                        class="border border-red-500 border-dashed p-2 text-xs font-bold text-red-500"
+                    >
+                        WARNING: The recipient is a smart contract. Sending ETH
+                        or tokens directly to a contract may result in permanent
+                        loss of funds.
+                    </div>
+                </div>
+                <div
+                    id="confirm-burn-warning"
+                    class="mb-2"
+                    style="visibility: hidden"
+                >
+                    <div
+                        class="border border-red-500 border-dashed p-2 text-xs font-bold text-red-500"
+                    >
+                        WARNING: This is a known null/burn address. Funds sent
+                        here are permanently destroyed and cannot be recovered.
+                    </div>
+                </div>
                 <div
                     id="confirm-errors"
                     class="mb-2 border border-border border-dashed p-2"