feat(ecash): adopt the reference NUT-02 resolver + real/test network switch

Executes steps 1-3 of docs/cashu-cdk-migration-plan.md, plus the test-coin
switch needed to exercise these routes without spending real sats.

Protocol layer: depend on `cashu` 0.17.5 (MIT, the crate CDK is built on,
default-features off, `wallet` only). Keyset ids now go through upstream's
`Id::from_short_keyset_id` / `ShortKeysetId` instead of the prefix match
hand-rolled in 2277fc46 — same repair, but implemented by the reference
code that defines the rule, so the next spec turn is a version bump rather
than another incident. `MintClient` feeds it the mint's `/v1/keysets` in
upstream's own `KeySetInfo` shape, parsing entries individually so one
keyset in an unmodelled unit can't block resolving the id we need.

Adding the crate required relaxing `bip39 = "=2.1.0"` to `"2.1"` (resolves
2.2.2): the exact pin held `unicode-normalization` at 0.1.22 and no
resolution existed otherwise. The pin carried no recorded rationale; seed
tests cover the bump.

Network switch: `wallet.ecash-network` / `wallet.ecash-set-network`, with a
Test mode toggle in Wallet Settings → Cashu. Cashu has no testnet, so this
points the wallet at the public `testnut` mint — but crucially each network
gets its OWN wallet and accepted-mints file, because test and real proofs
in one purse would be spendable interchangeably and the balance would be a
lie. Mainnet keeps the original filenames, so existing funds files are
untouched and switching is reversible: tests assert a real balance survives
a round trip through test mode.

Headless coverage: scripts/test-ecash-routes.sh drives every ecash RPC over
the real HTTP path (network get/set, balance, history, mint quote + claim,
send, receive, double-redeem refusal, garbage input, melt quote), restores
the node's original network on exit, and exits non-zero with the failure
count.

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

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

@@ -36,6 +36,51 @@ impl RpcHandler {
         }))
     }
 
+    /// `wallet.ecash-network` — which ecash network this node is on, and the
+    /// balance sitting in the *other* one so the UI can say what switching
+    /// would reveal rather than appearing to lose money.
+    pub(super) async fn handle_wallet_ecash_network(&self) -> Result<serde_json::Value> {
+        let current = ecash::load_network(&self.config.data_dir).await;
+        let wallet = ecash::load_wallet(&self.config.data_dir).await?;
+        Ok(serde_json::json!({
+            "network": current,
+            "is_test": current.is_test(),
+            "mint_url": wallet.mint_url,
+            "balance_sats": wallet.balance(),
+        }))
+    }
+
+    /// `wallet.ecash-set-network` — switch between real and test ecash.
+    ///
+    /// Each network keeps its own wallet file, so this never moves, merges or
+    /// deletes coins: switching away parks the current balance and switching
+    /// back finds it exactly as it was.
+    pub(super) async fn handle_wallet_ecash_set_network(
+        &self,
+        params: Option<serde_json::Value>,
+    ) -> Result<serde_json::Value> {
+        let params = params.ok_or_else(|| anyhow::anyhow!("Missing params"))?;
+        let requested = params
+            .get("network")
+            .and_then(|v| v.as_str())
+            .ok_or_else(|| anyhow::anyhow!("Missing network ('mainnet' or 'testnet')"))?;
+        let network = match requested {
+            "mainnet" => ecash::EcashNetwork::Mainnet,
+            "testnet" => ecash::EcashNetwork::Testnet,
+            other => anyhow::bail!("Unknown ecash network '{other}' — use 'mainnet' or 'testnet'"),
+        };
+
+        ecash::save_network(&self.config.data_dir, network).await?;
+        let wallet = ecash::load_wallet(&self.config.data_dir).await?;
+        tracing::info!(?network, "ecash network switched by operator");
+        Ok(serde_json::json!({
+            "network": network,
+            "is_test": network.is_test(),
+            "mint_url": wallet.mint_url,
+            "balance_sats": wallet.balance(),
+        }))
+    }
+
     pub(super) async fn handle_wallet_ecash_mint(
         &self,
         params: Option<serde_json::Value>,