feat(fullnode): auto-reconcile wallet after bootstrap; runtime rescan for pruned nodes

A wallet bootstrapped from a snapshot keeps its wallet.dat but never rescans, so
its spent-state is stale and the first send tries to spend already-spent notes and
is rejected. The startup -rescan flag can't fix it either: the snapshot lacks the
pre-snapshot block history -rescan needs, so it errors. The working fix is a runtime
rescanblockchain RPC from a height the snapshot actually has.

- Add App::runtimeRescan(startHeight): runs rescanblockchain via the worker, drives
  the rescanning UI state, and owns completion via the RPC callback (getrescaninfo
  is unavailable on this daemon). Suppresses the per-second mining/rescan pollers
  and the Core/balance/tx refreshes while the daemon holds cs_main for the scan.
- Add App::detectLowestAvailableBlockHeight(): async binary search via getblock for
  the lowest height whose block data is on disk → the snapshot base, and whether the
  node still has full history.
- Auto-reconcile after bootstrap: both completion sites (wizard + Settings download
  dialog) mark a pending rescan; once the daemon is back up and the tip is known,
  detect the base and runtimeRescan() from it (or -rescan restart on a full node).
- Settings "Rescan Blockchain" now probes first: full-history nodes get the existing
  -rescan restart; bootstrapped/pruned nodes get a prompt pre-filled with the
  detected base height that runs the runtime rescan.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/util/i18n.cpp

@@ -418,6 +418,9 @@ void I18n::loadBuiltinEnglish()
         strings_["confirm_rescan_title"] = "Rescan Blockchain";
         strings_["confirm_rescan_msg"] = "This restarts the daemon and re-scans the entire blockchain for your wallet's transactions. It can take a long time and the wallet stays offline until it finishes.";
         strings_["confirm_rescan_safe"] = "Your wallet.dat and blockchain data are not deleted — only re-scanned.";
+        strings_["rescan_detecting"] = "Checking which blocks your node has on disk…";
+        strings_["rescan_bootstrapped_msg"] = "Your node was bootstrapped, so blocks below the snapshot aren't on disk and a rescan from genesis would fail. Rescan from a height your snapshot includes to reconcile your wallet's spent balance. Your wallet.dat and chain data are not deleted.";
+        strings_["rescan_from_height"] = "Rescan from block height:";
         strings_["repair_wallet"] = "Repair Wallet";
         strings_["tt_repair_wallet"] = "Wipe and rebuild the wallet's transaction records from the blockchain (fixes notes that fail to send after a rescan)";
         strings_["confirm_repair_wallet_title"] = "Repair Wallet";