fix: Sign & Send refuses a transfer reviewed on another network (closes #524)

Settings is reachable from the confirmation screen, and Back from it only
unhides the screen as it was drawn. Sign & Send took the network at the
click, so a transfer reviewed on Sepolia went out on mainnet after a switch
in between. show() now records the chain id of the network it draws for.
Sign & Send refuses with a message on the screen when the active network
differs, and the send carries that chain id, so ethers will not populate it
for a provider on any other network.

Model: opus-5-5

README.md

@@ -1641,6 +1641,12 @@ view would leave a wallet one click from deletion.
       the contract's own answer is read at signing time only to be compared with
       it, and a disagreement is a refusal rather than a preference for either
       value (`src/shared/transferAmount.js`)
+    - "Sign & Send" after the active network was switched in Settings while this
+      screen was open → nothing is signed; "The active network changed after
+      this transaction was reviewed, so it was not sent. Please go back and
+      review it again." in the errors box, no screen change. The transaction
+      carries the chain id of the network the screen was shown for, so it cannot
+      be signed for another
     - "Sign & Send" (wrong password) → "Wrong password." on the password error
       line, no screen change
     - "Back" → **Send**