feat(graph): Add TOML-based graph configuration loader

Allow pipelines to be defined in TOML format with intuitive
node-and-connection syntax that's easy to read and edit.

- Add graph_toml.py with TOML parsing using tomllib
- Support simple format: "source": "headlines"
- Support full format: {"type": "camera", "mode": "scroll"}
- Parse connection strings in "A -> B -> C" chain format
- Add example pipeline_graph.toml demonstrating usage

Example TOML:
[nodes.source]
type = "source"
source = "headlines"

[nodes.camera]
type = "camera"
mode = "scroll"

[connections]
list = ["source -> camera -> display"]

examples/pipeline_graph.toml

@@ -0,0 +1,28 @@
+# Graph-based pipeline configuration example
+# This defines a pipeline using the new graph DSL
+
+[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 = 0.8
+
+[nodes.display]
+type = "display"
+backend = "null"
+
+[connections]
+list = ["source -> camera -> noise -> fade -> display"]