fix: ensure exported images reflect recent style and configuration changes

[ppmpreetham]

📑 Summary

This PR fixes a bug where exporting an image after changing the diagram's configuration (styles) would result in an image with the old styles. It ensures that changes made in the Config editor correctly trigger a diagram update so the exported image reflects the latest state.

📏 Design Decisions

Previously, when the diagram text was changed, updateCode properly triggered the updateDiagram: true flag. However, when the configuration was changed, the updateConfig function in src/lib/util/state.ts only updated the config string without setting the updateDiagram flag. Because of this, the exportImage function was relying on a stale render state, causing it to export the previous version of the diagram.

To fix this, I updated the updateConfig function to include updateDiagram: true, mirroring the behavior of updateCode. This explicitly signals the application to refresh the render cycle when styles are modified.

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added unit/e2e tests (if appropriate)
• 🔖 targeted develop branch

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