fix: show balances and fees below 0.000001 ETH as nonzero on the send screens (closes #343)

The stored ETH balance and the send-confirm screen's fee were each cut to six
decimal places, so a value below 0.000001 read as 0.0. The ETH balance is now
stored exactly, and the send and send-confirm screens' balances, reserve and
insufficient-balance messages go through truncateAmountNeverZero(). Both the
send-confirm and approval screens render the fee through formatFee(), which
prices the exact fee in USD, so the same fee reads the same on both. Token
balances keep their six-decimal value: it also leaves dust off the balance
list, and keeps the string within the 18 decimals the balance check reads.

Model: opus-5-5

TODO.md

@@ -45,6 +45,20 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-04: The Send and confirmation screens no longer show an ETH balance or
+  a network fee below 0.000001 as `0.0`
+  ([#343](https://git.eeqj.de/sneak/AutistMask/issues/343)). The stored ETH
+  balance (`src/shared/balances.js`) and the confirmation screen's fee were each
+  cut to six decimal places by a rule of their own. The ETH balance is now
+  stored exactly, and the Send screen's `Current balance`, and the confirmation
+  screen's balance, fee, reserve and insufficient-balance messages, go through
+  `truncateAmountNeverZero()` in `src/shared/amountDisplay.js`, the helper the
+  approval screen already used. The confirmation and approval screens both
+  render the fee through `formatFee()` in `src/popup/views/helpers.js`, which
+  prices the exact fee in USD, so the same fee reads the same on both, USD value
+  included. Token balances are still stored to six decimal places: that cut is
+  also what leaves a holding below 0.000001 off the balance list, and keeps the
+  stored string within the 18 decimals the balance check reads.
 - 2026-10-03: The typed-data signing screen warns for a token permission, and
   names the primary type ethers signs
   ([#400](https://git.eeqj.de/sneak/AutistMask/issues/400)). A Permit or Permit2