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).

tests/test_figment_effect.py

@@ -0,0 +1,103 @@
+"""
+Tests for the FigmentOverlayEffect plugin.
+"""
+
+import pytest
+
+from engine.effects.plugins import discover_plugins
+from engine.effects.registry import get_registry
+from engine.effects.types import EffectConfig, create_effect_context
+from engine.pipeline.adapters import EffectPluginStage
+
+
+class TestFigmentEffect:
+    """Tests for FigmentOverlayEffect."""
+
+    def setup_method(self):
+        """Discover plugins before each test."""
+        discover_plugins()
+
+    def test_figment_plugin_discovered(self):
+        """Figment plugin is discovered and registered."""
+        registry = get_registry()
+        figment = registry.get("figment")
+        assert figment is not None
+        assert figment.name == "figment"
+
+    def test_figment_plugin_enabled_by_default(self):
+        """Figment plugin is enabled by default."""
+        registry = get_registry()
+        figment = registry.get("figment")
+        assert figment.config.enabled is True
+
+    def test_figment_renders_overlay(self):
+        """Figment renders SVG overlay after interval."""
+        registry = get_registry()
+        figment = registry.get("figment")
+
+        # Configure with short interval for testing
+        config = EffectConfig(
+            enabled=True,
+            intensity=1.0,
+            params={
+                "interval_secs": 0.1,  # 100ms
+                "display_secs": 1.0,
+                "figment_dir": "figments",
+            },
+        )
+        figment.configure(config)
+
+        # Create test buffer
+        buf = [" " * 80 for _ in range(24)]
+
+        # Create context
+        ctx = create_effect_context(
+            terminal_width=80,
+            terminal_height=24,
+            frame_number=0,
+        )
+
+        # Process frames until figment renders
+        for i in range(20):
+            result = figment.process(buf, ctx)
+            if len(result) > len(buf):
+                # Figment rendered overlay
+                assert len(result) > len(buf)
+                # Check that overlay lines contain ANSI escape codes
+                overlay_lines = result[len(buf) :]
+                assert len(overlay_lines) > 0
+                # First overlay line should contain cursor positioning
+                assert "\x1b[" in overlay_lines[0]
+                assert "H" in overlay_lines[0]
+                return
+            ctx.frame_number += 1
+
+        pytest.fail("Figment did not render in 20 frames")
+
+    def test_figment_stage_capabilities(self):
+        """EffectPluginStage wraps figment correctly."""
+        registry = get_registry()
+        figment = registry.get("figment")
+
+        stage = EffectPluginStage(figment, name="figment")
+        assert "effect.figment" in stage.capabilities
+
+    def test_figment_configure_preserves_params(self):
+        """Figment configuration preserves figment_dir."""
+        registry = get_registry()
+        figment = registry.get("figment")
+
+        # Configure without figment_dir
+        config = EffectConfig(
+            enabled=True,
+            intensity=1.0,
+            params={
+                "interval_secs": 30.0,
+                "display_secs": 3.0,
+            },
+        )
+        figment.configure(config)
+
+        # figment_dir should be preserved
+        assert "figment_dir" in figment.config.params
+        assert figment.config.params["figment_dir"] == "figments"