feat(node): detect an unreadable block DB on startup and offer a one-click reindex

When a daemon update changes the block-index on-disk format (or the index is
corrupt), dragonxd aborts at startup — "non-canonical optional discriminant" →
"Error loading block database. Aborted." — and the wallet silently shows a zero
balance. Previously the connect loop just crash-restarted into the same abort up
to 3x and then reported a bare "Daemon crashed N times", with no path forward.

Now:
- daemon/daemon_startup_diagnosis.h: pure blockDbOutputLooksBroken() classifies
  the crashed node's captured console output (the fatal block-DB markers).
- The connect loop detects it on the FIRST abort, STOPS crash-restarting into the
  same failure (each retry reloads the whole index — wasteful), and offers a fix.
- A one-shot -reindex flag (EmbeddedDaemon::setReindexOnNextStart → DaemonController
  forwarder → args) rebuilds the block index + chainstate from the intact raw
  blocks; App::reindexBlockDatabase() arms it and un-gates the loop to restart.
- An auto-shown dialog (renderBlockDbReindexDialog) + a notification explain the
  situation ("your coins are safe; the node just can't load the chain") and offer
  a one-click "Rebuild block database". Full-node only (gated), lite-safe.

This is the exact trap behind a real "big wallet shows no funds" report: a
post-format-change daemon over pre-change chaindata. Reindex also fixes a plain
corrupt index.

Adds testBlockDbOutputDiagnosis (the abort sequence + individual markers trip it;
normal startup / wallet-corruption / asmap errors do not). Suite green (1/1).

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

src/daemon/daemon_startup_diagnosis.h

@@ -0,0 +1,30 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+//
+// daemon_startup_diagnosis.h — pure classifiers over a crashed daemon's captured console output,
+// so the app can offer a targeted one-click fix instead of a bare "daemon crashed" / silent no-funds.
+
+#pragma once
+
+#include <string>
+
+namespace dragonx {
+namespace daemon {
+
+// True when dragonxd aborted because its BLOCK DATABASE could not be loaded — either a
+// daemon-vs-chaindata serialization-format mismatch after a daemon update (the deterministic
+// "non-canonical optional discriminant" → "Error loading block database" → "Aborted block database
+// rebuild. Exiting." sequence) or a genuinely corrupt/incomplete block index. In BOTH cases the fix
+// is the same: `-reindex` rebuilds the index + chainstate from the intact raw blocks (blk*.dat).
+// This is what otherwise silently presents as a wallet with zero balance — the node never starts.
+inline bool blockDbOutputLooksBroken(const std::string& out)
+{
+    return out.find("Error loading block database")        != std::string::npos
+        || out.find("non-canonical optional discriminant") != std::string::npos
+        || out.find("Aborted block database rebuild")      != std::string::npos
+        || out.find("LoadBlockIndex()")                    != std::string::npos;  // "... : failed to read value"
+}
+
+}  // namespace daemon
+}  // namespace dragonx