fix: use theme-aware msg_gradient for ntfy messages

Replace lr_gradient_opposite() with msg_gradient() in render_message_overlay().
Messages now render in complementary colors matching the active theme:
- Green theme → magenta messages
- Orange theme → blue messages
- Purple theme → yellow messages

engine/layers.py

@@ -18,7 +18,7 @@ from engine.effects import (
     noise,
     vis_trunc,
 )
-from engine.render import big_wrap, lr_gradient, lr_gradient_opposite
+from engine.render import big_wrap, lr_gradient, msg_gradient
 from engine.terminal import RST, W_COOL
 
 MSG_META = "\033[38;5;245m"
@@ -57,7 +57,7 @@ def render_message_overlay(
     else:
         msg_rows = msg_cache[1]
 
-    msg_rows = lr_gradient_opposite(
+    msg_rows = msg_gradient(
         msg_rows, (time.monotonic() * config.GRAD_SPEED) % 1.0
     )