fix(lnd): SendPaymentV2 needs an explicit fee budget — absent means ZERO

v1.8.9's move to Router.SendPaymentV2 shipped without fee_limit_sat,
and the v2 route treats an ABSENT fee limit as zero allowed fees.
Every real route carries a routing fee (the 2-hop route here: 1.5
sats), so the pathfinder rejected them all and the wallet answered
"No route to the recipient" on EVERY send — all day, on healthy
channels with plenty of liquidity both ways.

The router debug log makes it unambiguous:
  wallet payment (v1.8.9 backend): fee_limit=0 mSAT     -> no route
  same payment by hand (lncli --fee_limit=100): fee_limit=100000 mSAT -> settles in 0.65s

My earlier "pipeline verified" claim was wrong — the manual lncli
verification set a fee limit by hand and masked this exact bug. The
400k that succeeded this morning went through the pre-update backend
on the pre-update LND.

Payments now carry lncli's own default budget — the payment amount
(100%), preferring the payer-supplied amount for zero-value invoices
and the invoice's own amount otherwise, with a nominal floor so the
limit can never be zero. Unit-pinned so it cannot regress.

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## v1.8.10-alpha (2026-09-02)
 
+- **Lightning sends work again — v1.8.9's payment switch lost the fee budget.** Moving payments to LND 0.21's supported route (Router.SendPaymentV2) shipped without a fee limit, and the v2 API treats an absent limit as **zero allowed fees**: every real route carries a routing fee, so the pathfinder rejected them all and the wallet answered "No route to the recipient" on every send — all day, on healthy channels with plenty of liquidity. The router debug log made it unambiguous (`fee_limit=0 mSAT` on every failing wallet payment; the same payment succeeded by hand the moment a fee limit was set). Payments now carry lncli's default budget (the payment amount), the wallet's amount handling for zero-value invoices is preserved, and a unit test pins the limit can never be zero again.
+
 - **A channel that drops its peer link now heals itself — on every node.** Restarting LND (an app update, a reboot, container churn) can leave a channel's peer connection down for hours while both endpoints keep the channel flagged disabled in the routing graph: the node looks perfectly healthy, the wallet shows balance, and every payment in either direction fails "no route to the recipient". Observed live: a node's only channel sat unroutable for ~17 hours after the LND 0.21.2 update, with no sign of it in any dashboard. The daemon now watches the channel graph as desired state — every open channel should have a live peer — and reconnects any that don't, using the peer's advertised addresses. Nodes without LND are untouched; an unreachable peer is retried gently, not hammered.
 
 - **The Lightning wallet states the node's real funding state instead of "you have no channel."** Trying to send while a freshly opened channel was still waiting for on-chain confirmations — or when all its balance sits on the far side — raised a modal that claimed the node had NO channel at all (the outbound sum is legitimately zero in both states), pointed the user at opening a second channel, and — for payment routing failures — even showed the *receiving* copy. The funding gate now reads the channel list it already fetched: a confirming channel gets "it unlocks automatically once confirmed, nothing is needed from you", a far-side balance gets "you can receive, but there's nothing to send right now", a routing/liquidity payment failure says so instead of claiming channel problems, and only a genuinely channel-less node keeps the open-one guidance.