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

The README's amount-display section carried a claim that contradicted the
tree: it said a genuine zero renders `0.0000`, but a swap's `Min. received`
worked example now shows `None (no minimum guaranteed)` for a zero minimum.
The claim is corrected — it holds for the ERC-20 amount, while the swap's
`Amount` and `Min. received` state their two misleading zeros (a V4 open
delta and a zero minimum) in words before the floor is reached.

A new list names every string an amount slot can show and what each means:
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 was checked against the
tree. Docs only; no code or tests change.

Model: opus-4-8

TODO.md

@@ -132,6 +132,18 @@ but the review is broader than any of them.
   constant rather than `isDebug()`, so it survives only in a debug build; a
   testnet or the runtime debug toggle still raises the banner but without the
   view id.
+- 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, but the swap's `Amount` and `Min. received` state their two
+  misleading zeros in words upstream. 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