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/popup/views/settingsAddToken.js

@@ -12,7 +12,7 @@ function isTracked(address) {
     return state.trackedTokens.some((t) => t.address.toLowerCase() === lower);
 }
 
-function tokenLabel(t) {
+function nameAndSymbol(t) {
     return t.name ? t.name + " (" + t.symbol + ")" : t.symbol;
 }
 
@@ -60,7 +60,7 @@ function renderDropdown() {
     let html = '<option value="">-- select --</option>';
     for (const t of tokens) {
         const tracked = isTracked(t.address);
-        const label = tokenLabel(t) + (tracked ? " (tracked)" : "");
+        const label = nameAndSymbol(t) + (tracked ? " (tracked)" : "");
         html +=
             `<option value="${escapeHtml(t.address)}"` +
             ` data-symbol="${escapeHtml(t.symbol)}"` +