test: cover every control that refuses a defective wallet (closes #254)

Each control that leads to a signature or to the private key now has a
test that it refuses a defective wallet before decrypting anything: Send
on the main, address and token screens, Export Private Key, and both
approval screens, as drawn and as clicked.

Send on the confirmation screen had no such check. The Send buttons
stand in front of it, but the popup reopens onto it from a saved view,
so it now refuses the same way.

The comments that said the wallet's key cannot be derived now say that
getSignerForAddress refuses it, and the walletDefects module comment
names both earlier import paths.

Model: opus-5-5

src/shared/walletDefects.js

@@ -13,11 +13,17 @@ const NON_MASTER_XPRV = "non-master-xprv";
 
 // An "xprv" wallet stores the neutered BIP-44 Ethereum node, four levels below
 // the key that was imported: the current import path derives the absolute
-// m/44'/60'/0'/0 from a depth-0 key, and the pre-#210 path derived the same
-// four levels as a relative path beneath whatever depth it was given. A master
-// import therefore stores a depth-4 xpub and a depth-d import stores depth
-// d + 4, which makes the stored xpub an exact read on the imported key's
-// depth — and it is readable without the password, unlike the key itself.
+// m/44'/60'/0'/0 from a depth-0 key, and the path before #210 (57959b7)
+// derived the same four levels as a relative path beneath whatever depth it
+// was given. A master import therefore stores a depth-4 xpub and a depth-d
+// import stores depth d + 4, which makes the stored xpub an exact read on the
+// imported key's depth — and it is readable without the password, unlike the
+// key itself.
+//
+// The first import path (7a7f9c5) does not fit: it stored the imported key's
+// own xpub with no derivation, so a wallet it wrote is judged wrongly here (a
+// master import as defective, a depth-4 import as sound). 57959b7 replaced it
+// in the same push, and no tag contains it.
 const BIP44_ETH_XPUB_DEPTH = 4;
 
 const DEFECTS = {