fix: say an unknown-scale balance the same way on Send and on confirm (closes #377)

When two addresses' explorer reports disagree on a token's decimals, the
Send screen showed the stored figure while the confirmation screen said
the balance was unknown. One function in send.js now gives both the
balance and scale, so both read `unknown (SYMBOL)`.

The confirmation screen's fee-unknown message names its cause: for an
unknown scale it says the wallet does not know the token's decimal
places and the transaction cannot be sent, instead of asking for a
retry that cannot help. Other causes keep the old sentence.

Model: opus-5-5

README.md

@@ -949,6 +949,13 @@ and compare against. Reading the stored field directly instead answers `null`
 for a bundled or tracked token the explorer merely omitted, which is not a
 refusal the wallet has any reason to make.
 
+The Send screen also consults every address's explorer reports, so a contract
+two addresses report different `decimals` for has no scale there, and the stored
+balance, formatted at one of those scales, is withdrawn with it. The Send
+screen's `Current balance` and the confirmation screen's balance line then both
+read `unknown (SYMBOL)`. The balance list formats each explorer row as it is
+fetched, without that cross-address check, and shows the row's figure.
+
 **Decoded amount lines on the transaction approval screen:** the `Amount` line
 of a decoded ERC-20 call, and the `Amount` and `Min. received` lines of a
 decoded swap (see TxApproval below), do not always read as a number. They can
@@ -1409,7 +1416,9 @@ view would leave a wallet one click from deletion.
     - What to send: token dropdown (or static display with contract address when
       locked from AddressToken)
     - To: address or ENS name input, with an inline validation message
-    - Amount input with current balance display
+    - Amount input with current balance display, which reads
+      `Current balance: unknown (SYMBOL)` for a token whose scale is unknown, as
+      ConfirmTx's balance line does (see Unknown token scale)
     - "Review" button, disabled until the recipient validates
 - **Transitions**:
     - "Review" (valid inputs, ENS resolved) → **ConfirmTx**
@@ -1427,7 +1436,8 @@ view would leave a wallet one click from deletion.
     - From: blockie + color dot + full address + etherscan link + wallet title
     - To: blockie + color dot + full address + etherscan link + ENS name
     - Amount: value + symbol (USD in parentheses)
-    - Your balance: value + symbol (USD in parentheses)
+    - Your balance: value + symbol (USD in parentheses), or `unknown (SYMBOL)`
+      for a token whose scale is unknown
     - Network fee: "Estimating..." then two lines, or "Unable to estimate",
       fetched async. The first line is what the transfer is expected to cost,
       `gasLimit * gasPrice` (USD in parentheses); the second is the
@@ -1443,7 +1453,11 @@ view would leave a wallet one click from deletion.
       amount plus the fee exceeds the balance (ETH transfers), not enough ETH to
       pay the fee for the transfer (ERC-20 transfers), and the fee could not be
       estimated. The first two are mutually exclusive per transfer type, so only
-      the applicable one holds space
+      the applicable one holds space. The last names its cause: for a token
+      whose scale is unknown the fee can never be estimated, and it says the
+      wallet does not know how many decimal places the token uses and that the
+      transaction cannot be sent; for any other failure it asks the user to go
+      back and try again
     - Password: an inline field on this screen, not a modal, with its own error
       line
     - "Sign & Send" button (disabled if errors, and while the network fee