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/embedded_daemon.cpp

@@ -571,6 +571,14 @@ bool EmbeddedDaemon::start(const std::string& binary_path)
         args.push_back("-rescan");
     }
 
+    // -reindex rebuilds the block index + chainstate from the raw blocks (fixes an unreadable/format-
+    // mismatched block DB). It's about the CHAIN, not the wallet, so it's independent of the wallet-repair
+    // chain above (and implies its own wallet rescan). One-shot, consumed here.
+    if (reindex_on_next_start_.exchange(false)) {
+        DEBUG_LOGF("[INFO] Adding -reindex flag to rebuild the block database from raw blocks\n");
+        args.push_back("-reindex");
+    }
+
     // One-shot isolated-datadir override (migrate-to-seed flow): run this start against a
     // throwaway datadir, plus any extra args (e.g. -connect=0). Consumed here so later starts
     // revert to the normal datadir. The datadir's basename MUST be the assetchain name (DRAGONX)