Add getting started guide and demo dataset generator

Rewrote PIPELINE_ILLUSTRATION.md as a practical getting-started guide focused on data generation workflow. Added generate_demo_dataset.py to provide a working example that generates, validates, and saves a small syndrome dataset. These changes make it easier for new users to understand and use the package.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ChanceSiyuan

.claude/settings.local.json

@@ -0,0 +1,9 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(gh issue view:*)",
+      "Bash(gh pr comment:*)",
+      "Bash(gh run view:*)"
+    ]
+  }
+}