feat(wallet): Ark protocol support via barkd sidecar

barkd (Ark wallet daemon, pinned 0.3.0, checksum-verified release binary)
packaged as an installable app; thin HTTP bridge in wallet/ark_client.rs
mirrors the fedimint_client pattern — the bark SDK stays out of the node
binary. wallet.ark-* RPCs cover status/balance/address/send/invoice/
board/offboard/history/configure; Ark movements merge into the unified
ecash history (kind="ark") and spendable Ark sats into total_sats.
Signet defaults (Second's public Ark server) until Ark matures.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/wallet.rs

@@ -1,5 +1,5 @@
 use super::RpcHandler;
-use crate::wallet::{ecash, fedimint_client, profits};
+use crate::wallet::{ark_client, ecash, fedimint_client, profits};
 use anyhow::Result;
 
 /// A Cashu token (NUT-00 `cashuA`/`cashuB`, or our legacy `cashuSend_` form)
@@ -21,13 +21,16 @@ impl RpcHandler {
                 Ok(client) => client.total_balance_sats().await.unwrap_or(0),
                 Err(_) => 0,
             };
+        // Spendable Ark (barkd) balance, same best-effort contract.
+        let ark_sats = ark_client::spendable_sats_or_zero(&self.config.data_dir).await;
         Ok(serde_json::json!({
             // `balance_sats` stays Cashu-only for back-compat; `total_sats` is the
-            // spendable amount across Cashu + Fedimint.
+            // spendable amount across Cashu + Fedimint + Ark.
             "balance_sats": cashu_sats,
             "cashu_sats": cashu_sats,
             "fedimint_sats": fedimint_sats,
-            "total_sats": cashu_sats + fedimint_sats,
+            "ark_sats": ark_sats,
+            "total_sats": cashu_sats + fedimint_sats + ark_sats,
             "proof_count": wallet.proofs.iter().filter(|p| !p.spent && !p.reserved).count(),
             "mint_url": wallet.mint_url,
         }))
@@ -181,6 +184,8 @@ impl RpcHandler {
         let wallet = ecash::load_wallet(&self.config.data_dir).await?;
         let mut transactions = wallet.transactions;
         transactions.extend(fedimint_client::load_fedimint_txs(&self.config.data_dir).await);
+        // Ark movements from barkd (kind="ark"), best-effort like Fedimint.
+        transactions.extend(ark_client::load_ark_txs(&self.config.data_dir).await);
         // Sort by RFC-3339 timestamp descending (string compare is valid for
         // same-offset RFC-3339), newest first.
         transactions.sort_by(|a, b| b.timestamp.cmp(&a.timestamp));