api: optional prefix param on the four marketplace listings

[On1x]

The node gained an optional trailing argument on these four read methods (viz-cpp-node steemit#160) that is matched against an index, so a filter can reach rows the caller never paged to. The API explorer advertised the old signatures.

Documented in all three places the explorer and the lib read from:

• src/api/methods.js — the method tree the lib generates its wrappers from
• api-frontend/app.js — its copy of that tree plus the SPEC descriptions
• api-frontend/jsonrpc-api-spec.json — the canonical spec

method	new arg
database_api.get_accounts_on_sale	name_prefix
database_api.get_accounts_on_auction	name_prefix
database_api.get_subaccounts_on_sale	name_prefix
paid_subscription_api.get_paid_subscriptions	creator_prefix

Empty or omitted keeps the old behaviour, and the explorer does not send an empty value at all, so nothing changes for a caller that ignores the argument.

Before the next release

The generated wrappers read the callback from a fixed position (args[params.length]), so adding a param is breaking for positional callers — getPaidSubscriptions(0, 100, cb) would hand cb over as the prefix. Callers using the *With(options, cb) form are unaffected: an absent option serialises to null, which the node treats as an empty prefix (verified on mainnet).

Nothing in Forecaster-client or WebVIZWallet calls these four positionally, so the break only reaches external npm consumers, and only when a release is cut — which is a separate, deliberate step (npm publish is irreversible). Flagging it here so that step is not taken blind.

Live

api.viz.world already serves this app.js, and the explorer was driven end-to-end against mainnet: with name_prefix empty the first page is press, liveblogs, russia, finance, bitcoin; with pre it is press alone.

Follows steemit#160, which shipped code-only.