Accept LNURL-pay invoices without matching description_hash

[martinsaposnic]

Summary

• Removes the LUD-06 description_hash check in HTTPHrnResolver::resolve_lnurl_to_invoice so BOLT11 invoices with a plain d tag (or a mismatched h tag) are accepted instead of being rejected with "BOLT 11 invoice resolved via LNURL must have a matching description hash".
• Motivated by real-world non-compliant LNURL-pay servers (e.g. bringin.xyz) which mint invoices with d = "Topup 22000 sats" and no h tag. Strike pays these fine; upstream bitcoin-payment-instructions does not, so moneydevkit payouts to these addresses fail.

Targets 2025-12-ldk-node-base (the branch mdkd and ldk-node pin via rev 6796e87) instead of main, so a single rev bump in those consumers picks up the fix without dragging in the LDK version drift between this branch and main.

Tradeoff

LUD-06 requires the invoice's h tag to commit to sha256(metadata) so the payer's wallet can prove the invoice it signs matches the metadata it displayed. Dropping the check means a malicious or buggy LNURL host can swap the invoice description out from under the user. We accept this here to unblock payouts. Callers that want the spec-correct behavior should use upstream.

Test plan

• cargo build --features http clean on this branch
• cargo build clean on lightning-js with its bitcoin-payment-instructions dep swapped to this branch (the only build error encountered was a pre-existing, unrelated LSPS4ServiceEvent::SendWebhook field mismatch in local ldk-node/rust-lightning working trees)
• Live test against vincenzopalazzo@bringin.xyz via HTTPHrnResolver:

  Resolving vincenzopalazzo@bringin.xyz for 23000000 msat
    min=Some(22098000 milli-satoshis)
    max=Some(15453023000 milli-satoshis)
    description=Some("Payment to vincenzopalazzo@bringin.xyz")
  
  set_amount: OK
    BOLT11 invoice: lnbc230u1p4qkjf0pp5lr89jlckmwvc8vlpfxdwck6h2p79xmw9hawjka6w3qrr0q8ueyfq...
    amount_msat: Some(23000000)
    payment_hash: f8ce597f16db9983b3e1499aec5b57507c536dc5bf5d2b774e88063780fcc912
    description: Direct(Description(UntrustedString("Topup 23000 sats")))
  

  Note description: Direct(...) is exactly the case upstream rejects; this fork passes through.

Followups (not in this PR)

• After merge, bump rev in lightning-js, ldk-node, and mdkd to the new SHA so all three resolve to a single copy of this crate.
• Replaces PR Accept LNURL-pay invoices without matching description_hash #1, which was opened against main by mistake.