docs: name every approval-screen amount string, fix stale zero claim (closes #369)

The README's amount-display section claimed a genuine zero always renders
`0.0000`. That is corrected and scoped: it holds for the ERC-20 amount and for
the swap's `Amount` line on a literal-zero `amountIn` in a V2/V3 exact-in swap
or a zero `WRAP_ETH`. Only two zeros are stated in words before the floor — the
swap's `Min. received` (any zero minimum) and its V4 exact-in `Amount` (an
`amountIn` of zero, V4's open delta).

A new list names every string an amount slot can show: a formatted quantity,
`Unlimited`, `All available (V4 open delta)`, `None (no minimum guaranteed)`,
base units with decimals unknown, and `Unknown (not named in the calldata)`. It
also records that a zero `minBalance` on a `BALANCE_CHECK_ERC20` step now reads
the no-minimum wording where it once read `0.0000`. Each claim checked against
the tree. Docs only.

Model: opus-4-8

TODO.md

@@ -143,6 +143,21 @@ but the review is broader than any of them.
   both routes take, so they behave the same and the button is live for the next
   delete.
 
+- 2026-09-21: `README.md` now documents the approval screen's amount-slot
+  vocabulary and no longer contradicts itself
+  ([#369](https://git.eeqj.de/sneak/AutistMask/issues/369)). The stale claim
+  that a genuine zero still renders `0.0000` is corrected: it holds for the
+  ERC-20 amount, and also for the swap's `Amount` line on a literal-zero
+  `amountIn` in a V2/V3 exact-in swap or a zero `WRAP_ETH`. Only two zeros are
+  stated in words upstream — the swap's `Min. received` (any zero minimum) and
+  its V4 exact-in `Amount` (an `amountIn` of zero, V4's open delta). The
+  amount-display section now names every string a slot can show — a formatted
+  quantity, `Unlimited`, `All available (V4 open delta)`,
+  `None (no minimum guaranteed)`, base units with decimals unknown, and
+  `Unknown (not named in the calldata)` — and records that a zero `minBalance`
+  on a `BALANCE_CHECK_ERC20` step now reads `None (no minimum guaranteed)` where
+  it once read `0.0000`. Docs only; each claim checked against the tree.
+
 - 2026-08-30: An address no longer wraps, or is shortened to fit, in any of the
   common views ([#380](https://git.eeqj.de/sneak/AutistMask/issues/380)). The
   wallet list was the reported case: the address shared one row with the