Define and Validate Final config Schema for Custom Dashboards

The config field on Analytics::CustomDashboard currently accepts any JSON object, and validation is limited to ensuring the root value is a Hash. The final structure of the dashboard configuration is still evolving, so the existing JSON schema (custom_dashboard_config.json) is only a placeholder.

We need to define the final schema for config and update the JSON schema validation accordingly.

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Problem

• The API currently accepts any arbitrary JSON shape.
• The JSON schema validator enforces structure, but the actual schema is not yet defined.
• As the dashboard feature evolves (e.g., layout, widgets, metadata), the schema must be formalized to prevent invalid configurations from being stored.
• We rely on a custom Ruby validator to ensure config is a JSON object, which should eventually be enforced by the JSON schema alone.

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Proposal

• Define the full expected structure of the config object, including:
  • Top-level keys (e.g., layout, widgets, metadata)
  • Type definitions for all fields
  • Allowed values
  • Required vs optional fields
• Update custom_dashboard_config.json to reflect the finalized schema.
• Remove or simplify the custom Ruby validator once the JSON schema enforces the correct structure.
• Add model specs to confirm invalid configurations are properly rejected.