chore: remove dead exports and share copied view helpers (closes #168)

AddressDetail and AddressToken defined their own isoDate() and
timeAgo(), hiding the shared pair in helpers.js, so a fix there would
not have reached them. The copies were identical and are deleted;
blockieHtml() and tokenLabel(), each defined twice, move to helpers.js.
A new test shows the history rows and the transaction detail view
write the time with the shared pair.

Deleted as never called: explorerLink(), ETHEREUM_SEPOLIA_CHAIN_ID,
getWalletValue() and getTotalValue() with their tests. Home's "Total:"
is the active address's total, as README.md already says.
addressColor() and etherscanAddressUrl() are no longer exported.

Model: opus-5-5

src/shared/prices.js

@@ -104,27 +104,6 @@ function getAddressValue(addr) {
     return { usd, partial };
 }
 
-// The same pair for a whole wallet, and for every wallet at once. One
-// unpriced holding anywhere makes the sum a floor, so partial carries up.
-function getWalletValue(wallet) {
-    return sumValues(wallet.addresses.map(getAddressValue));
-}
-
-function getTotalValue(wallets) {
-    return sumValues(wallets.map(getWalletValue));
-}
-
-function sumValues(values) {
-    let usd = null;
-    let partial = false;
-    for (const value of values) {
-        if (value.usd === null) continue;
-        usd = (usd === null ? 0 : usd) + value.usd;
-        partial = partial || value.partial;
-    }
-    return { usd, partial };
-}
-
 // The one rendering of an address total, so no screen says it differently.
 //
 // A partial total is shown and named as partial: the figure is the ETH and
@@ -149,6 +128,4 @@ module.exports = {
     formatUsd,
     formatAddressTotal,
     getAddressValue,
-    getWalletValue,
-    getTotalValue,
 };