Optimize startup: show black overlay first, dim brightness in a background thread; switch to one-folder PyInstaller build (no on-launch extraction)

- black screen now appears immediately (window creation), while the slow
  screen-brightness-control WMI queries (get+set) run in a daemon thread and
  are invisible behind the black overlay
- one-folder COLLECT build removes the ~2-3s one-file archive extraction

black_screen_dim.py

@@ -13,9 +13,12 @@ import logging
 import os
 import sys
 import tempfile
+import threading
 
 import screen_brightness_control as sbc
 
+_original_brightness = None
+
 LOG = logging.getLogger("black_screen_dim")
 
 
@@ -354,14 +357,24 @@ if sys.platform == "win32":
                 break
 
 
+def _dim_and_save():
+    """Save current brightness and dim all monitors in the background so the
+    black overlay can appear instantly; the dimming itself is invisible."""
+    global _original_brightness
+    orig = get_all_brightness()
+    _original_brightness = orig
+    LOG.info("saved brightness: %s", orig)
+    if orig is not None:
+        set_all_brightness(0)
+
+
 def main():
     setup_logging()
     LOG.info("starting Black Screen Dim")
-    original = get_all_brightness()
-    LOG.info("saved brightness: %s", original)
-    if original is not None:
-        set_all_brightness(0)
-
+    # Show the black overlay FIRST so the screen goes black immediately.
+    # Brightness saving/dimming runs in the background, invisible behind it.
+    dim_thread = threading.Thread(target=_dim_and_save, daemon=True)
+    dim_thread.start()
     try:
         if sys.platform == "win32":
             run_overlay()
@@ -370,9 +383,11 @@ def main():
     except Exception as e:
         LOG.exception("overlay error: %r", e)
     finally:
-        if original is not None:
-            restore_all_brightness(original)
-        LOG.info("restored brightness: %s", original)
+        dim_thread.join(timeout=10)
+        orig = _original_brightness
+        if orig is not None:
+            restore_all_brightness(orig)
+        LOG.info("restored brightness: %s", orig)
         LOG.info("exiting")