fix(wallet): surface silent save failures + stale-state cleanups (W5-1, W5-2, W6-1, W6-3)

P2 robustness batch (localized):

- W5-1 (Med, lite): persistAfterBroadcast returned false on a persistent post-send/shield
  save failure, but both callers discarded it and it never logged — completely silent. It
  now liteLogs the failure (the spent note re-derives on the next sync, so it's a
  robustness gap, not fund loss).

- W5-2 (Med, lite): the post-sync and post-rescan save results (in the detached scan
  threads) were ignored; both now liteLog on failure. LiteDiagnostics::log is mutex-guarded,
  so it's safe from those threads.

- W6-1 (Med): WalletState::clear() didn't reset mining/pool_mining, so a wallet switch could
  briefly show the previous wallet's hashrate/blocks. Now reset in clear() (the daemon
  restarts on switch, so mining genuinely stops).

- W6-3 (Low): AddressBook::load() cleared entries_ then threw on the first non-object array
  element — discarding EVERY contact. It now guards is_object() + per-entry try/catch,
  skipping and counting malformed entries.

Build-clean; ctest 1/1. Remaining P2: W6-2 (refresh-staleness badge — needs UI, overlaps
the diagnostics Foundation bundle). See docs/wallet-hardening.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/wallet/lite_wallet_controller.cpp

@@ -80,8 +80,10 @@ bool persistAfterBroadcast(LiteClientBridge& bridge)
     for (int attempt = 0; attempt < 2; ++attempt) {
         if (bridge.execute("save", "").ok) return true;
     }
-    // Persistent failure: the spent note will be re-derived from the chain on the next sync,
-    // so this is a robustness gap, not fund loss. (Retry handles the common transient case.)
+    // Persistent failure: the spent note will be re-derived from the chain on the next sync, so this
+    // is a robustness gap, not fund loss. Log it (W5-1) — both callers discard this return, so the
+    // failure was previously completely silent.
+    liteLog("save failed after send/shield — the wallet will re-derive it on the next sync");
     return false;
 }
 
@@ -600,7 +602,8 @@ void LiteWalletController::startSync()
             // The backend does NOT auto-save after a sync, so persist the freshly-scanned wallet;
             // otherwise the next launch re-scans from the checkpoint (~30 min). Set `done` only
             // after the save so a syncComplete() observer sees a fully-persisted wallet.
-            bridge->execute("save", "");
+            if (!bridge->execute("save", "").ok)   // W5-2: don't leave a failed post-sync save silent
+                liteLog("save failed after sync — the next launch will re-scan from the checkpoint");
         }
         done->store(true);
     });
@@ -631,7 +634,8 @@ bool LiteWalletController::startRescan()
             // `rescan` clears the wallet's synced block cache and re-downloads/re-scans from the
             // birthday height — a blocking, uninterruptible full scan, same as `sync`.
             bridge->execute("rescan", "");
-            bridge->execute("save", "");  // backend doesn't auto-save after a rescan
+            if (!bridge->execute("save", "").ok)   // W5-2: don't leave a failed post-rescan save silent
+                liteLog("save failed after rescan — the next launch will re-scan from the checkpoint");
         }
         done->store(true);
     });