fix: the balance lists and Home cut amounts to four decimals (closes #757)

The balance lists and Home's ETH line rounded with toFixed(4), so 0.99996
ETH read 1.0000 there and 0.9999 on Send. They now cut the stored decimal
string with truncateAmount(), as the history rows do. balanceLine() takes
the stored balance string instead of a parsed number, and escapes the
quantity cell. The screens that state what is authorized keep the floor
of truncateAmountNeverZero().

Model: opus-5-5

tests/approvalDisplayFloor.test.js

@@ -25,10 +25,6 @@ const { ERC20_ABI } = require("../src/shared/constants");
 const { state } = require("../src/shared/state");
 const { decodeCalldata } = require("../src/shared/calldataDecoder");
 const uniswap = require("../src/shared/uniswap");
-const {
-    truncateAmount,
-    truncateAmountNeverZero,
-} = require("../src/shared/amountDisplay");
 
 const iface = new Interface(ERC20_ABI);
 
@@ -183,15 +179,4 @@ describe("the four-decimal rule is otherwise unchanged", () => {
     test("a genuine zero still renders as zero", () => {
         expect(amount(transferData(0n), DAI).rawValue).toBe("0.0000");
     });
-
-    // The three truncators now share one module. The floor is a policy of the
-    // approval and confirmation screens only: the history and balance lists
-    // keep plain truncation, because the transaction detail view is the
-    // authoritative record and already shows exact precision.
-    test("the list rule stays unfloored", () => {
-        expect(truncateAmount("0.000000000000000001")).toBe("0.0000");
-        expect(truncateAmountNeverZero("0.000000000000000001")).toBe(
-            "0.000000000000000001",
-        );
-    });
 });