v0.47.0 — account mode stops guessing

Account mode stops guessing. 0.46.0 shipped API-key billing with one honest
limitation: it could not tell you what a call cost or how much credit was left,
so it printed a local estimate with a ~ and a dashboard link. The account API
gained both signals today, and this release consumes them.

blockrun_wallet action:"status" now reads the real balance from
GET /v1/credits:

  Account:  acme (ungated)
  Spent to date: $4.5239 (invoiced account — no prepaid ceiling)

A prepaid account shows Credit remaining: $12.50 of $50.00 granted; a blocked
one says so, and why, before you spend a call discovering it. A read failure
degrades to the session figure rather than failing the whole status call.

Per-call costs are now the settled amount, not an estimate, everywhere the
account API reports one: search, exa, surf, markets, rpc, defi,
phone, modal, music, speech, video, realface. That is not cosmetic —
BLOCKRUN_BUDGET_LIMIT and the per-agent delegate caps book what they are
told, and they were booking an estimate that ran high by exactly the transaction
fee this rail does not charge. A 19-character speech render now books $0.000998
where it used to book $0.0031. blockrun_chat keeps its estimate, because chat
settles after the response by design and holding the answer until the money
landed would be a worse trade; anything still estimated prints a ~ and says so.

Getting there meant routing account calls around the SDK. On that rail there is
no 402 to perform — no quote, nothing to sign, no retry-after-payment — so
requestWithPaymentRaw degrades to a fetch with a Bearer header, which
utils/api-key-call.ts already does, and does better: it reads the response
instead of discarding it. utils/raw-call.ts is now the single place that picks
a rail, so eight path-based tools stopped choosing one for themselves. Wallet
calls still go through the SDK, where the 402 dance is real work worth not
reimplementing.

Two traps worth naming, because both read as success.

Number("") is 0, not NaN. A present-but-empty cost header parsed with a
bare Number() would book $0 against a genuinely billed call — the exact
confusion the header exists to remove, reintroduced in the reader. Empty,
malformed and negative all read as absent; an explicit 0.000000 is preserved,
because a charge that really settled at zero is not the same as no charge
settling at all.

remaining_usd ?? 0 would tell a paying customer in good standing that they are
broke. An invoiced account legitimately has no prepaid ceiling, so remaining is
null and the correct thing to show is spend-to-date. Two independent clients hit
this within a day of the endpoint shipping.

blocked_reason is a code, not a message, so it is mapped to a remedy here —
ACCOUNT_SUSPENDED must not advise topping up, which would not lift it. An
unrecognised code degrades to naming the code rather than reading as "not
blocked", which would send an agent on to a call the proxy has already refused.

Tests 449 → 458.