Implement ETH send and QR code receive

Send: stores mnemonic/private key with wallet data, derives
signing key from mnemonic + address index via ethers HDNodeWallet,
constructs transaction with parseEther, broadcasts via
sendTransaction, waits for confirmation, shows block number
and tx hash. ENS resolution in To field preserved.

Receive: QR code rendered to canvas via qrcode library (1.5.4).
Shows scannable QR above the full address text.

README updated with qrcode dependency and TODO progress.

package.json

@@ -21,6 +21,7 @@
     },
     "dependencies": {
         "ethers": "^6.16.0",
-        "libsodium-wrappers-sumo": "^0.8.2"
+        "libsodium-wrappers-sumo": "^0.8.2",
+        "qrcode": "^1.5.4"
     }
 }