feat(figment): complete pipeline integration with native effect plugin

- Add engine/effects/plugins/figment.py (native pipeline implementation)
- Add engine/figment_render.py, engine/figment_trigger.py, engine/themes.py
- Add 3 SVG assets in figments/ (Mexican/Aztec motif)
- Add engine/display/backends/animation_report.py for debugging
- Add engine/pipeline/adapters/frame_capture.py for frame capture
- Add test-figment preset to presets.toml
- Add cairosvg optional dependency to pyproject.toml
- Update EffectPluginStage to support is_overlay attribute (for overlay effects)
- Add comprehensive tests: test_figment_effect.py, test_figment_pipeline.py, test_figment_render.py
- Remove obsolete test_ui_simple.py
- Update TODO.md with test cleanup plan
- Refactor test_adapters.py to use real components instead of mocks

This completes the figment SVG overlay feature integration using the modern pipeline architecture, avoiding legacy effects_plugins. All tests pass (758 total).

engine/figment_trigger.py

@@ -0,0 +1,36 @@
+"""
+Figment trigger protocol and command types.
+
+Defines the extensible input abstraction for triggering figment displays
+from any control surface (ntfy, MQTT, serial, etc.).
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from enum import Enum
+from typing import Protocol
+
+
+class FigmentAction(Enum):
+    TRIGGER = "trigger"
+    SET_INTENSITY = "set_intensity"
+    SET_INTERVAL = "set_interval"
+    SET_COLOR = "set_color"
+    STOP = "stop"
+
+
+@dataclass
+class FigmentCommand:
+    action: FigmentAction
+    value: float | str | None = None
+
+
+class FigmentTrigger(Protocol):
+    """Protocol for figment trigger sources.
+
+    Any input source (ntfy, MQTT, serial) can implement this
+    to trigger and control figment displays.
+    """
+
+    def poll(self) -> FigmentCommand | None: ...