feat(figment): add test fixture SVG and FIGMENT_TRIGGER event type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

engine/events.py

@@ -18,6 +18,7 @@ class EventType(Enum):
     NTFY_MESSAGE = auto()
     STREAM_START = auto()
     STREAM_END = auto()
+    FIGMENT_TRIGGER = auto()
 
 
 @dataclass
@@ -65,3 +66,12 @@ class StreamEvent:
     event_type: EventType
     headline_count: int = 0
     timestamp: datetime | None = None
+
+
+@dataclass
+class FigmentTriggerEvent:
+    """Event emitted when a figment is triggered."""
+
+    action: str
+    value: float | str | None = None
+    timestamp: datetime | None = None