fix(fullnode): reliable rescan completion + self-explaining shielded send errors

Two related fixes for the post-bootstrap "send fails / rescan stuck at 99%" trap:

1) Rescan completion now keys off warmup-end. A -rescan runs entirely inside daemon
   warmup (every RPC returns -28 until it finishes), so warmup completing IS the rescan
   completing. The old detectors relied on getrescaninfo (which some daemons answer with
   "Method not found") or a "Done rescanning"/bench log line the daemon may never print,
   leaving the status bar stuck at 99% — so users killed the rescan before it finished.
   When warmup ends and a rescan was confirmed active, clear the rescan state, flip to
   100%, refresh history/balance, and toast completion.

2) z_sendmany failures that mean stale shielded note data (shielded-requirements-not-met,
   missing sapling anchor, invalid sapling spend proof, bad-txns-sapling-*) now append a
   plain-language hint telling the user to run a full rescan, instead of surfacing only the
   raw daemon string.

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

src/app_network.cpp

@@ -1144,6 +1144,26 @@ void App::refreshCoreData()
                     state_.warmup_description.clear();
                     connection_status_ = TR("connected");
                     VERBOSE_LOGF("[warmup] Daemon ready, warmup complete\n");
+
+                    // A -rescan runs entirely INSIDE daemon warmup (every RPC returns -28 until the
+                    // scan finishes), so warmup completing IS the rescan completing. This is the
+                    // reliable completion signal: some daemons lack getrescaninfo (it returns
+                    // "Method not found") or never print a "Done rescanning"/bench line, which left
+                    // the older detectors stuck at 99% — the user would then kill it prematurely.
+                    // rescan_confirmed_active_ ensures we actually observed this rescan running (set
+                    // by the getrescaninfo / daemon-log pollers) before declaring it done.
+                    if (state_.sync.rescanning && rescan_confirmed_active_) {
+                        state_.sync.rescanning = false;
+                        rescan_confirmed_active_ = false;
+                        state_.sync.rescan_progress = 1.0f;
+                        state_.sync.rescan_status.clear();
+                        // Notes/witnesses were rebuilt — force a fresh history + balance pull.
+                        transactions_dirty_ = true;
+                        last_tx_block_height_ = -1;
+                        invalidateShieldedHistoryScanProgress(true);
+                        ui::Notifications::instance().success("Blockchain rescan complete");
+                    }
+
                     NetworkRefreshService::applyConnectionInfoResult(state_, result.info);
                     // Trigger full data refresh now that daemon is ready
                     refreshData();