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/shared/symbolSpoof.js

@@ -11,8 +11,8 @@
 // KNOWN_SYMBOLS maps a symbol to the set of lowercased contract addresses
 // that may bear it, or to null.  Null means the symbol belongs to the native
 // asset, which has no contract at all, so no contract may bear it and every
-// one that does is a spoof.  "ETH" is the only such entry today; the rule is
-// written so that a second one needs no change here or at any call site.
+// one that does is a spoof.  "ETH" is one such entry, and every network's
+// `nativeCurrency` in networks.js (`SepoliaETH`) is another, on every network.
 //
 // The value is a set because a ticker is not unique: seven symbols in the
 // bundled list belong to two real contracts each, and answering with one of