feat: Implement Chart Builder feature with UI and functionality

- Added a new modal for the Chart Builder to allow users to create visualizations from datasets.
- Integrated chart builder state management and validation for encoding configurations.
- Implemented auto-selection of default fields based on dataset column types.
- Added live preview functionality for real-time chart rendering.
- Created a new JavaScript file (chart-builder.js) to handle chart building logic.
- Updated app.js to initialize the chart builder and handle URL state changes.
- Enhanced styles in styles.css for the chart builder UI components.
- Documented the implementation details in project-docs/chart-builder-implementation.md.

.claude/settings.local.json

@@ -0,0 +1,9 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(node --check:*)"
+    ],
+    "deny": [],
+    "ask": []
+  }
+}