Never roll back an ambiguous broadcast as if it had been refused (B-76, TX-04, TX-05, TX-20, TX-21, BET-16, BET-17, BET-23, WDR-11, WDR-12, WDR-16, API-13)

place_bet and request_withdrawal released everything on any exception from the
broadcast, including the 15s timeout and a connection dropped after the write. The
tx may have propagated: a bet's sats landed in the pool with no participant, a
withdrawal left while its row said failed and its coins were spendable again.

- client: ElectrumRpcError (subclass of ElectrumError) is raised only for a reply
  carrying a JSON-RPC `error`; timeouts, drops and write errors stay plain
  ElectrumError.
- tx/outcome.py:broadcast_with_verdict sorts a broadcast into accepted / refused /
  uncertain. A refusal is verified first: ElectrumListener.transaction_known asks
  blockchain.transaction.get of the active server and every other one (10s each) —
  any server returning the tx means accepted; the active server plus
  MIN_QUORUM_RESPONSES others all denying it means refused (ALLOW_NO_QUORUM keeps
  the reduced rule); too few answers is uncertain. "already known" wording is only a
  shortcut that skips the check. With no network to ask, a refusal is uncertain.
- place_bet / request_withdrawal / _trigger_payout use it: only a verified refusal
  releases; uncertain leaves the rows building for the reconciler, publishes SSE and
  POST /bets and POST /withdrawals answer 202 with status building; "already known"
  promotes a payout (payout_sent) like any accepted broadcast.
- An accepted transaction is fanned out to every other server
  (ElectrumListener.fan_out_transaction, best effort, off the caller's path). The RBF
  replacement in bump_fee is left for B-77, which rewrites that function.

Tests changed because the spec changed: the existing "refused broadcast" tests raised
a bare RuntimeError (now an uncertain outcome) and are made explicit refusals
(rpc_error) with a network that denies the tx; direct route calls pass a Response;
FakePayoutListener gains the network surface.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/api.md

@@ -220,10 +220,7 @@ esiste una API separata per l'amministrazione, solo un'autenticazione diversa.
   "già noto / già nel mempool" vale come successo (`201`).
   *Codice:* `app/api/routes/bets.py:create_bet`,
   `app/api/routes/withdrawals.py:create_withdrawal` ·
-  *Test:* `tests/unit/test_bets.py`
-  *Stato:* da implementare (B-76) · *Oggi:* qualunque eccezione del broadcast,
-  compresi il timeout di 15 s e la caduta della connessione, annulla tutto e
-  risponde `502 broadcast_failed`.
+  *Test:* `tests/unit/test_bets.py`, `tests/unit/test_broadcast_outcome.py`
 
 - **[API-14]** Qualunque eccezione non gestita risponde `500` con lo stesso
   formato strutturato, codice `internal_error`, messaggio
@@ -471,9 +468,7 @@ esiste una API separata per l'amministrazione, solo un'autenticazione diversa.
   *Codice:* `app/api/routes/bets.py:create_bet`,
   `app/bets/service.py:place_bet` ·
   *Test:* `tests/unit/test_bets.py`
-  *Stato:* da implementare (B-76, B-95, B-96) · *Oggi:* ogni esito diverso
-  dal successo è `502 broadcast_failed` con tutto annullato; la trasmissione
-  va solo al server attivo; un costo coperto solo da resto non confermato
+  *Stato:* da implementare (B-95, B-96) · *Oggi:* un costo coperto solo da resto non confermato
   risponde `insufficient_balance`; non c'è tetto al montepremi; il costo è
   quello configurato al momento della scommessa, non quello del round.
 
@@ -521,9 +516,7 @@ esiste una API separata per l'amministrazione, solo un'autenticazione diversa.
   *Codice:* `app/api/routes/withdrawals.py:create_withdrawal`,
   `app/withdrawals/service.py:request_withdrawal` ·
   *Test:* `tests/unit/test_withdrawals.py`
-  *Stato:* da implementare (B-76, B-96) · *Oggi:* ogni esito diverso
-  dal successo è `502 broadcast_failed` con il prelievo `failed`; la
-  trasmissione va solo al server attivo; l'importo ridotto di un prelievo
+  *Stato:* da implementare (B-96) · *Oggi:* l'importo ridotto di un prelievo
   dell'intero saldo non è riconfrontato con il minimo.
 
 ### Round