feat(preset): Add enable_message_overlay to presets

- Add enable_message_overlay field to PipelinePreset dataclass
- Enable message overlay in demo, ui, and firehose presets
- Add test-message-overlay preset for testing
- Update preset loader to support new field from TOML files

presets.toml

@@ -62,6 +62,7 @@ effects = []  # Demo script will add/remove effects dynamically
 camera_speed = 0.1
 viewport_width = 80
 viewport_height = 24
+enable_message_overlay = true
 
 [presets.demo-pygame]
 description = "Demo: Pygame display version"
@@ -72,6 +73,7 @@ effects = []  # Demo script will add/remove effects dynamically
 camera_speed = 0.1
 viewport_width = 80
 viewport_height = 24
+enable_message_overlay = true
 
 [presets.demo-camera-showcase]
 description = "Demo: Camera mode showcase"
@@ -82,6 +84,18 @@ effects = []  # Demo script will cycle through camera modes
 camera_speed = 0.5
 viewport_width = 80
 viewport_height = 24
+enable_message_overlay = true
+
+[presets.test-message-overlay]
+description = "Test: Message overlay with ntfy integration"
+source = "headlines"
+display = "terminal"
+camera = "feed"
+effects = ["hud"]
+camera_speed = 0.1
+viewport_width = 80
+viewport_height = 24
+enable_message_overlay = true
 
 # ============================================
 # SENSOR CONFIGURATION