feat(node): warn when the daemon auto-recovers (salvages) wallet.dat

dragonxd auto-recovers a wallet.dat that fails BDB verification on startup — no
flag needed (CWallet::Verify → CDBEnv::Verify(walletFile, CWalletDB::Recover)):
it moves the original to wallet.<timestamp>.bak, salvages readable keys into a
fresh wallet.dat, and keeps running. The salvage can be incomplete (or the whole
thing a FALSE POSITIVE from stale/cross-platform BDB env state — __db.* / the
database/ dir carried between machines), so the node silently comes up on a
possibly-empty wallet. To the user that reads as fund loss, with no warning.

Detect it and warn loudly instead:
- daemon/daemon_startup_diagnosis.h: pure walletAutoRecovered() (the salvage /
  "Original wallet.dat saved as wallet.<ts>.bak" markers) + newestWalletSalvageBak()
  (picks the wallet.<unixtime>.bak the recovery just made).
- onConnected() scans the node's captured output once per session; on a match it
  shows a warning dialog + notification: the ORIGINAL is safe in wallet.<ts>.bak,
  the shown balance may be incomplete, and here are the exact steps to restore it
  (rename the .bak back + delete the stale database/ + __db.* env). One-click
  "Open data folder" jumps straight there. Full-node only; lite-safe.

Deliberately does NOT auto-swap the wallet files (untested per-platform file
manipulation on a real wallet is not worth the risk) — it informs + guides.

Adds walletAutoRecovered / newestWalletSalvageBak coverage to
testBlockDbOutputDiagnosis. Suite green (1/1).

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

src/app.h

@@ -900,6 +900,12 @@ private:
     // connect loop STOPS crash-restarting into the same abort and offers a one-click reindex instead.
     bool block_db_reindex_available_ = false;   // node needs its block DB rebuilt (gates restart loop)
     bool show_block_db_reindex_confirm_ = false; // auto-shown offer dialog
+    // Wallet auto-recovery: the daemon moved wallet.dat to wallet.<ts>.bak and loaded a salvaged copy
+    // (BDB-verify failure — often a false positive from stale/cross-platform env state). We warn loudly
+    // so a possibly-incomplete salvaged wallet isn't mistaken for fund loss. Warned once per session.
+    bool wallet_auto_recovered_ = false;         // a salvage happened this session
+    bool wallet_auto_recovered_warned_ = false;  // guard: only surface it once per session
+    bool show_wallet_recovered_dialog_ = false;  // auto-shown warning dialog
     // Live progress for the switch modal: it stays open from confirm through stop → wait-for-exit → start →
     // reconnect and auto-closes when the new node connects (onConnected). Phase is worker-updated;
     // dialog_open_ gates rendering — both atomic since onConnected/the worker may run off the main thread.
@@ -1331,6 +1337,7 @@ private:
     void renderSwitchStopDaemonDialog();  // confirm before stopping an adopted node to switch wallets
     void renderBlockDbReindexDialog();    // offer to rebuild an unreadable block database (-reindex)
     void reindexBlockDatabase();          // restart the daemon with -reindex to rebuild the block DB
+    void renderWalletRecoveredDialog();   // warn that the node auto-recovered/salvaged wallet.dat
     void processDeferredEncryption();
 
     // Private methods - connection