fix(ecash): stop replayed Minibits claims retrying forever, reduce relay churn

claim_and_redeem retried every redeem failure indefinitely, including a
terminal one: mint error 11001 "Token Already Spent" (a claim replayed by a
relay-watermark edge case, or already redeemed by an earlier run). On
archy-x250-pa3 this pinned pending_claims at 1 forever and hammered
mint.minibits.cash's swap endpoint every ~6s, with the UI permanently
showing "a payment arrived but couldn't be redeemed yet".

- mint_client: expose the NUT error-code-11001 message as
  ALREADY_REDEEMED_MSG so callers can recognize it without duplicating the
  string.
- minibits: drop (not retry) a redeem failure that matches
  is_already_redeemed — the value was already swept, so retrying can never
  succeed.
- fetch_relay_dms: query the primary relay.minibits.cash alone first,
  falling back to the public relay.damus.io/nos.lol only if it's
  unreachable, and page past a 200-DM backlog instead of silently
  stranding older DMs behind an un-advanced watermark.

This fix already existed on feat/minibits-lnurl-receive (4e410d7, 489995c,
2026-09-09) but that branch was never merged into main, which has its own
independently-diverged minibits.rs — so the bug shipped again in
1.8.16-alpha. Ported directly onto main's current implementation this time.

Immediate unblock on archy-x250-pa3: cleared the one poisoned
pending_claims entry from wallet/minibits.json by hand (already-redeemed,
zero value at risk) and restarted archipelago.service; confirmed via
journalctl that polling is quiet again.

See docs/incident-2026-09-15-minibits-already-redeemed.md for the full
writeup.

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

core/archipelago/src/wallet/mint_client.rs

@@ -71,10 +71,18 @@ pub struct MintResult {
 /// keyset codes shared by NUT-02/03/04/05 — the codes a swap/melt/mint call
 /// can actually hit. Returns `None` for anything else (e.g. Lightning/quote
 /// codes in the 20000s) so the caller falls back to the mint's own `detail`.
+///
+/// Text of the NUT error-code-11001 translation, exposed so callers that
+/// received an `anyhow::Error` from a receive/redeem path (e.g. a replayed
+/// Minibits claim) can recognize an already-spent token as terminal rather
+/// than retrying it forever.
+pub const ALREADY_REDEEMED_MSG: &str =
+    "This ecash has already been redeemed — it can't be claimed twice.";
+
 fn describe_mint_error_code(code: i64) -> Option<&'static str> {
     Some(match code {
         10001 => "The mint rejected these coins as invalid.",
-        11001 => "This ecash has already been redeemed — it can't be claimed twice.",
+        11001 => ALREADY_REDEEMED_MSG,
         11002 => "This ecash is already being redeemed elsewhere — try again in a moment.",
         11003 => "The mint already issued new coins for this exact request — there's nothing left to redeem.",
         11004 => "This request is still being processed by the mint — try again in a moment.",