Extends the fallback chain to: tb → state.trackedTokens → TOKEN_BY_ADDRESS → '?'
This ensures user-added custom tokens (not just hardcoded known tokens)
display correct symbol, name, and decimals even when Blockscout hasn't
returned balance data (e.g. zero-balance tracked tokens).
When a token's balance entry is missing or incomplete (e.g. not yet
fetched from Blockscout), the address-token view and send view now
fall back to the built-in known token list for symbol, name, and
decimals instead of showing '?'.
Also includes token name in the balance object returned by
fetchTokenBalances so the contract info well can display it.
Fixes#51
