fix(spv): clear stale SPV state and banner on RPC mode switch

When the backend switches from SPV to RPC without a full reset(),
stale spv_no_peers_since and spv_connected_peers values could persist,
causing the degraded timer to remain active incorrectly.

Additionally, the SPV degraded banner was only managed inside the
SPV mode branch, so switching away from SPV while the banner was
showing would leave it stuck on screen.

Fixes:
1. Clear SPV peer fields at the top of the RPC branch in
   refresh_zmq_and_spv().
2. Clear the SPV degraded banner unconditionally when not in SPV mode.

Author: thepastaclaw

src/context/connection_status.rs

@@ -459,6 +459,14 @@ impl ConnectionStatus {
                 }
             }
             CoreBackendMode::Rpc => {
+                // Clear stale SPV state that may linger if the backend mode
+                // switched from SPV to RPC without a full `reset()`.
+                self.spv_connected_peers.store(0, Ordering::Relaxed);
+                *self
+                    .spv_no_peers_since
+                    .lock()
+                    .unwrap_or_else(|e| e.into_inner()) = None;
+
                 // Update ZMQ status if there's a new event
                 let disable_zmq = app_context
                     .get_settings()