debug: add raw monitor write test after sync + fix boot window visible

manager/display.lua

@@ -1042,6 +1042,21 @@ function D.drawDashboard()
     -- Draw everything
     mainPage:draw()
     mainDevice:sync()
+
+    -- Debug: verify monitor is writable
+    if D._drawCount == nil then D._drawCount = 0 end
+    D._drawCount = D._drawCount + 1
+    if D._drawCount <= 3 then
+        log.info("DRAW", "sync complete (draw #%d, lines=%d, w=%d h=%d)",
+            D._drawCount,
+            mainDevice.lines and #mainDevice.lines or -1,
+            mainDevice.width or -1, mainDevice.height or -1)
+        -- Raw write test directly to the physical monitor
+        D.mon.setCursorPos(1, 1)
+        D.mon.setBackgroundColor(colors.red)
+        D.mon.setTextColor(colors.white)
+        D.mon.write("DRAW TEST #" .. D._drawCount)
+    end
 end
 
 function D.drawSmelterDashboard()