feat(examples): Add default visualization script

Add script that renders the standard Mainline visualization using the
graph-based DSL. This demonstrates the default behavior with:

- Headlines source data
- Scroll camera mode
- Terminal display
- Classic effects: noise, fade, glitch, firehose

Files added:
- examples/default_visualization.py - Main script
- examples/default_visualization.toml - TOML configuration
- examples/README.md - Documentation for all examples

Usage:
  python examples/default_visualization.py

examples/README.md

@@ -0,0 +1,87 @@
+# Examples
+
+This directory contains example scripts demonstrating how to use Mainline's features.
+
+## Default Visualization
+
+**`default_visualization.py`** - Renders the standard Mainline visualization using the graph-based DSL.
+
+```bash
+python examples/default_visualization.py
+```
+
+This script demonstrates:
+- Graph-based pipeline configuration using TOML
+- Default Mainline behavior: headlines source, scroll camera, terminal display
+- Classic effects: noise, fade, glitch, firehose
+- One-shot rendering (prints to stdout)
+
+### Configuration
+
+The visualization is defined in `default_visualization.toml`:
+
+```toml
+[nodes.source]
+type = "source"
+source = "headlines"
+
+[nodes.camera]
+type = "camera"
+mode = "scroll"
+speed = 1.0
+
+[nodes.noise]
+type = "effect"
+effect = "noise"
+intensity = 0.3
+
+[nodes.fade]
+type = "effect"
+effect = "fade"
+intensity = 0.5
+
+[nodes.display]
+type = "display"
+backend = "terminal"
+
+[connections]
+list = ["source -> camera -> noise -> fade -> display"]
+```
+
+## Graph DSL Demonstration
+
+**`graph_dsl_demo.py`** - Demonstrates the graph-based DSL in multiple ways:
+
+```bash
+python examples/graph_dsl_demo.py
+```
+
+Shows:
+- Imperative Python API for building graphs
+- Dictionary-based API
+- Graph validation (cycles, disconnected nodes)
+- Different node types and configurations
+
+## Integration Test
+
+**`test_graph_integration.py`** - Tests the graph system with actual pipeline execution:
+
+```bash
+python examples/test_graph_integration.py
+```
+
+Verifies:
+- Graph loading from TOML
+- Pipeline execution
+- Output rendering
+- Comparison with preset-based pipelines
+
+## Other Demos
+
+- **`demo-lfo-effects.py`** - LFO modulation of effect intensities (Pygame display)
+- **`demo_oscilloscope.py`** - Oscilloscope visualization
+- **`demo_image_oscilloscope.py`** - Image-based oscilloscope
+
+## Graph DSL Reference
+
+See `docs/graph-dsl.md` for complete documentation on the graph-based DSL syntax.