chore: the native token's label follows the network (closes #372)

networks.js gives each network a nativeCurrency (ETH, SepoliaETH) and nothing
read it: every screen wrote ETH. The wallet's balances and the Send and
confirmation screens now use the active network's. A transaction's figures use
the network its chain id names, through nativeCurrencyByChainId(): the
approval value and fee, the wait, success and error screens, history entries,
the detail screen and the fee-limit refusal, so a site switching networks
cannot make one read as another network's coin. The "ETH" that selectedToken
and txInfo.token hold is the native token's id and is unchanged. A token
reporting any network's nativeCurrency is a spoof, and the detail screen calls
an entry a token transfer when it has a token contract.

Model: opus-5-5

src/popup/index.html

@@ -640,19 +640,13 @@
                         Double-check the address before sending.
                     </div>
                 </div>
+                <!-- Its sentence names the network's native token, so show()
+                in confirmTx.js sets it. -->
                 <div
                     id="confirm-contract-warning"
-                    class="mb-2"
+                    class="mb-2 border border-red-500 border-dashed p-2 text-xs font-bold text-red-500"
                     style="visibility: hidden"
-                >
-                    <div
-                        class="border border-red-500 border-dashed p-2 text-xs font-bold text-red-500"
-                    >
-                        WARNING: The recipient is a smart contract. Sending ETH
-                        or tokens directly to a contract may result in permanent
-                        loss of funds.
-                    </div>
-                </div>
+                ></div>
                 <div
                     id="confirm-burn-warning"
                     class="mb-2"
@@ -690,14 +684,13 @@
                     Your balance does not cover this amount plus the network
                     fee. Please go back and send a smaller amount.
                 </div>
+                <!-- Its sentence names the network's native token, so show()
+                in confirmTx.js sets it. -->
                 <div
                     id="confirm-gas-error"
                     class="mb-2 border border-border border-dashed p-2 text-xs"
                     style="visibility: hidden"
-                >
-                    You do not have enough ETH to pay the network fee for this
-                    transfer. Please add ETH to this address and try again.
-                </div>
+                ></div>
                 <!-- Its sentence names why the fee could not be estimated,
                 so show() in confirmTx.js sets it. -->
                 <div