feat(wallet): subaddress provisioning and batched UTXO endpoints (off by default)

Backend support for two address-privacy features. Both are behind env flags
that default to off, so an unconfigured instance behaves exactly as before:
the routes are not mounted and no provisioning is attempted.

FEATURE_XMR_SUBADDR_PROVISIONING
  Adds POST /wallet/lws/provision_subaddrs and provisions account-0 subaddress
  indices on the LWS at register/import.

  Three money-safety properties worth calling out:

  * The provisioned ceiling is read from the LWS response, never echoed back
    from the request. It is the contiguous run starting at minor 0, not
    max(hi): given ranges [[0,99],[200,299]], reporting 299 would let a wallet
    hand out indices 100..199 that the LWS never scans, so funds sent there
    would be invisible. No usable run is a hard error, not a guess.
  * import_account now always runs the backward rescan even when provisioning
    fails. Previously a provisioning error aborted first, leaving the account
    registered at the chain tip while every retry returned 200 OK, so a
    restoring wallet would show a zero balance permanently.
  * A capacity probe reads max_subaddresses from the LWS and refuses up front
    with a message naming the required --max-subaddresses value, rather than
    failing per-account later. The option defaults to 0 upstream.

  Spent outputs now carry their subaddress index. monero-lws emits this as
  `sender` (the index the spent output was received at), not `recipient`;
  without it a client recomputes a primary key image for a subaddress spend,
  treats the mismatch as a decoy, and never subtracts the amount.

FEATURE_UTXO_MULTI_ADDRESS
  Adds balance_multi / utxos_multi / history_multi for HD gap-limit wallets.
  Capped at 32 addresses, summed with checked_add, per-UTXO address tag
  preserved so the client never has to re-guess which key owns an output.
  Bounded concurrency with a per-batch deadline returning 504, so a slow
  Electrum server cannot stack n * IO_TIMEOUT.

Both flags are advertised in /capabilities so a client can negotiate instead
of calling routes that 404.

src/api/openapi.rs

@@ -42,10 +42,14 @@ use utoipa::OpenApi;
         crate::api::wallet::btc_ltc::balance,
         crate::api::wallet::btc_ltc::utxos,
         crate::api::wallet::btc_ltc::history,
+        crate::api::wallet::btc_ltc::balance_multi,
+        crate::api::wallet::btc_ltc::utxos_multi,
+        crate::api::wallet::btc_ltc::history_multi,
         crate::api::wallet::btc_ltc::tip,
         crate::api::wallet::btc_ltc::fee,
         crate::api::wallet::btc_ltc::broadcast,
         crate::api::wallet::xmr_wow::register,
+        crate::api::wallet::xmr_wow::provision_subaddrs,
         crate::api::wallet::xmr_wow::balance,
         crate::api::wallet::xmr_wow::history,
         crate::api::wallet::xmr_wow::unspent_outs,
@@ -125,6 +129,12 @@ use utoipa::OpenApi;
         crate::api::wallet::btc_ltc::UtxosResponse,
         crate::api::wallet::btc_ltc::HistoryEntry,
         crate::api::wallet::btc_ltc::HistoryResponse,
+        crate::api::wallet::btc_ltc::MultiAddressRequest,
+        crate::api::wallet::btc_ltc::MultiBalanceResponse,
+        crate::api::wallet::btc_ltc::TaggedUtxo,
+        crate::api::wallet::btc_ltc::MultiUtxosResponse,
+        crate::api::wallet::btc_ltc::TaggedHistoryEntry,
+        crate::api::wallet::btc_ltc::MultiHistoryResponse,
         crate::api::wallet::btc_ltc::AssetRequest,
         crate::api::wallet::btc_ltc::TipResponse,
         crate::api::wallet::btc_ltc::FeeRequest,
@@ -133,11 +143,14 @@ use utoipa::OpenApi;
         crate::api::wallet::btc_ltc::BroadcastResponse,
         crate::api::wallet::xmr_wow::ViewRequest,
         crate::api::wallet::xmr_wow::RegisterRequest,
+        crate::api::wallet::xmr_wow::ProvisionRequest,
+        crate::api::wallet::xmr_wow::ProvisionResponse,
         crate::api::wallet::xmr_wow::RandomOutsRequest,
         crate::api::wallet::xmr_wow::SubmitRequest,
         crate::api::wallet::xmr_wow::LwsAssetRequest,
         crate::api::wallet::xmr_wow::ConfirmationsRequest,
         crate::api::wallet::xmr_wow::LwsBalanceResponse,
+        crate::api::wallet::xmr_wow::SubaddrIndexDto,
         crate::api::wallet::xmr_wow::SpentOutputDto,
         crate::api::wallet::xmr_wow::TxDto,
         crate::api::wallet::xmr_wow::LwsHistoryResponse,