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/pipeline/adapters/effect_plugin.py

@@ -27,9 +27,9 @@ class EffectPluginStage(Stage):
     def stage_type(self) -> str:
         """Return stage_type based on effect name.
 
-        HUD effects are overlays.
+        Overlay effects have stage_type "overlay".
         """
-        if self.name == "hud":
+        if self.is_overlay:
             return "overlay"
         return self.category
 
@@ -37,19 +37,26 @@ class EffectPluginStage(Stage):
     def render_order(self) -> int:
         """Return render_order based on effect type.
 
-        HUD effects have high render_order to appear on top.
+        Overlay effects have high render_order to appear on top.
         """
-        if self.name == "hud":
+        if self.is_overlay:
             return 100  # High order for overlays
         return 0
 
     @property
     def is_overlay(self) -> bool:
-        """Return True for HUD effects.
+        """Return True for overlay effects.
 
-        HUD is an overlay - it composes on top of the buffer
+        Overlay effects compose on top of the buffer
         rather than transforming it for the next stage.
         """
+        # Check if the effect has an is_overlay attribute that is explicitly True
+        # (not just any truthy value from a mock object)
+        if hasattr(self._effect, "is_overlay"):
+            effect_overlay = self._effect.is_overlay
+            # Only return True if it's explicitly set to True
+            if effect_overlay is True:
+                return True
         return self.name == "hud"
 
     @property