feat(dht): Phase 4 — paid swarm streaming (cross-mint ecash + Shape-A ALPN)

Fetch-side auto-pay decision layer (payment.rs), Shape-A paid-blobs
negotiation ALPN (paid_alpn.rs), cross-mint ecash swap + payer auto-swap
builder + idempotent resume/liquidity cache (ecash.rs), and the
streaming.prepare-payment RPC. All gated behind the iroh-swarm feature
(off by default). 91/91 tests pass, both build configs clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/archipelago/src/server.rs

@@ -164,6 +164,17 @@ impl Server {
             tracing::warn!("Swarm init (non-fatal, falling back to origin-only): {}", e);
         }
 
+        // Resume any cross-mint ecash swap interrupted by a previous crash
+        // (paid the source mint but never claimed the target tokens). Best-effort.
+        match crate::wallet::ecash::resume_pending_swaps(&config.data_dir).await {
+            Ok(0) => {}
+            Ok(reclaimed) => tracing::info!(
+                "Resumed interrupted cross-mint swaps: reclaimed {} sats",
+                reclaimed
+            ),
+            Err(e) => tracing::debug!("resume_pending_swaps (non-fatal): {}", e),
+        }
+
         // Revoke any previously published Nostr data (runs before publish so revocation is not overwritten)
         let identity_dir = config.data_dir.join("identity");
         let tor_proxy_revoke = config.nostr_tor_proxy.clone();