fix(lite-backend): record the mined height of mempool-first transactions

When the mempool monitor saw a transaction first, its wallet entry kept
the monitor's height (often 0) after the transaction was mined, because
scanning the block reused the entry without updating its block. A later
reorg between the two heights then left a phantom spend of our own
send and a change note with an empty witness list until a rescan.

Scanning a block now sets the entry's block to the block height. This
applies to every monitor-first transaction, including payments received
from others: their reported block height, the verified/spendable timing
that depends on it, and the wallet birthday now use the real mined
height instead of the monitor's.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

third_party/silentdragonxlite/silentdragonxlite-cli/lib/src/lightwallet.rs

@@ -2398,6 +2398,10 @@ pub fn scan_full_mempool_tx(&self, tx: &Transaction, height: i32, _datetime: u64
                 txs.insert(tx.txid, tx_entry);
             }
             let tx_entry = txs.get_mut(&tx.txid).unwrap();
+            // An existing entry can come from the mempool monitor (scan_full_mempool_tx), stamped with the
+            // height the server reported before the tx was mined. Record the block that mined it: a reorg of
+            // this block must remove the tx (invalidate_block and the witness clearing key on this field).
+            tx_entry.block = block_data.height;
             tx_entry.total_shielded_value_spent = total_shielded_value_spent;
 
             // Save notes.