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/constants.js

@@ -33,7 +33,6 @@ const DEBUG_MNEMONIC = DEBUG
     : null;
 
 const ETHEREUM_MAINNET_CHAIN_ID = "0x1";
-const ETHEREUM_SEPOLIA_CHAIN_ID = "0xaa36a7";
 
 const DEFAULT_RPC_URL = "https://ethereum-rpc.publicnode.com";
 
@@ -69,7 +68,6 @@ module.exports = {
     BUILD_DEBUG_MARKER,
     DEBUG_MNEMONIC,
     ETHEREUM_MAINNET_CHAIN_ID,
-    ETHEREUM_SEPOLIA_CHAIN_ID,
     DEFAULT_RPC_URL,
     DEFAULT_BLOCKSCOUT_URL,
     BIP44_ETH_PATH,