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

The README said a genuine zero always renders `0.0000`, beside a
`Min. received` example that now reads `None (no minimum guaranteed)`.
It now says which zeros are stated in words first: any zero
`Min. received`, and a zero V4 exact-in `amountIn` only when that step
sets the `Amount` line, since a Permit2 permit sets it whenever present.

A new list names every string an amount slot can show and when,
including a known-scale zero as `0.0000` and `Unlimited` for the
router's whole-balance value. It also records that a zero `minBalance`
on a `BALANCE_CHECK_ERC20` step now reads the no-minimum wording.
Docs only.

Model: opus-5-5

TODO.md

@@ -154,6 +154,22 @@ but the review is broader than any of them.
   standalone storage entry, never part of the versioned `autistmask` profile, so
   the state schema is untouched and no existing profile is affected.
 
+- 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 always renders `0.0000` is corrected: a zero with a known
+  scale does, except where the swap screen states it in words first —
+  `Min. received` always, and the `Amount` line only when a V4 exact-in of zero
+  is the step that sets it. A Permit2 permit sets that line whenever one is
+  present, so a zero permit, a zero V2/V3 exact-in `amountIn` or a zero
+  `WRAP_ETH` still reads `0.0000`. The amount-display section now names every
+  string a slot can show and when — a formatted quantity (a known-scale zero
+  included), `Unlimited` (on a swap also the router's whole-balance value),
+  `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.
+
 - 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