docs: README matches ConfirmTx's wrong-password message and fee-bound refusal (closes #610)

ConfirmTx shows "That password is incorrect. Please try again." for a
wrong password, as every other screen that asks for one does. README
quoted "Wrong password." instead.

The fee-bound refusal said the RPC endpoint always fills in the gas
limit and fees at signing. An ETH amount that Max filled in is signed
with the gas limit and fees of the screen's own fee estimate instead.
README now says so, and lists what assertWithinCeilings() checks.

Model: opus-5-5

README.md

@@ -2059,9 +2059,10 @@ view would leave a wallet one click from deletion.
       sent. Please go back and try again." in its own box, no screen change. For
       an ETH amount that Send's "Max" filled in, the gas limit and fees are
       those of this screen's own fee estimate (see Amount above). For any other
-      send, the RPC endpoint fills in the gas limit and fees at signing. Just
-      before signing, `assertWithinCeilings()` (`src/shared/approvalVerify.js`)
-      refuses the send when any of these is over its bound:
+      send, the RPC endpoint fills in the gas limit and fees at signing.
+      `assertWithinCeilings()` (`src/shared/approvalVerify.js`) checks the
+      transaction just before it is signed. The check refuses the send with the
+      sentence above when any of these is over its bound:
         - the gas limit
         - each fee per gas the transaction sets
         - the total fee: the gas limit times `maxFeePerGas`, or times `gasPrice`