fix(watchdog): handle LND restarts without locking outgoing operations

[PatMulligan]

Summary

• When LND restarts, the watchdog's cached payment index becomes stale, causing a false "History mismatch" that locks all
  outgoing operations
• Instead of immediately locking on a payment index advance, update the cached offset so the watchdog catches up to LND's
  actual state
• Only lock outgoing operations when both a history mismatch AND a balance discrepancy are detected — indicating a real
  security concern rather than a benign LND restart

Problem

The watchdog caches latestPaymentIndexOffset at startup. When LND restarts, the payment streams reconnect via Warmup(), but
this cache is never refreshed. The next watchdog check sees newLatest > knownMaxIndex and locks outgoing operations with
"History mismatch detected in absolute update, locking outgoing operations", even though the node balance is fine.

This means any LND restart (maintenance, crash recovery, upgrade) requires a manual Lightning.Pub restart to clear the lock.

Fix

In StartCheck(), when a payment index advance is detected:

1. Update latestPaymentIndexOffset to the new value (catch up)
2. Only lock if the balance check also fails (deny = true)
3. If balance is fine, log the index advance and continue operating

Test plan

• Restart LND while LP is running — verify LP logs "Payment index advanced" and continues operating
• Verify that a genuine balance discrepancy + history mismatch still triggers the lock
• Verify normal operation (no LND restart) is unaffected

LP logs from test

# LND restart detected — streams close
17:30:50 lndManager >> Error with subscribeHtlcEvents stream
17:30:50 lndManager >> Error with new block stream
17:30:50 lndManager >> invoice stream closed
17:30:50 lndManager >> LND is dead, will try to reconnect in 20 seconds
17:30:50 lndManager >> subscribeChannelEvents stream closed
17:30:50 lndManager >> onchain tx stream closed

# LND comes back — LP reconnects automatically
17:31:10 unlocker >> the wallet is already unlocked with pub: 03f0919c...
17:31:10 lndManager >> LND is back online

# First watchdog check after reconnect — no lock, no bark
17:31:39 updating tracked balance: 7944398

# Second check — still clean, operations remain unlocked
17:32:39 updating tracked balance: 7944398