Implement data-groups endpoint

[bburda]

Summary

Implement GET /apps/{id}/data-groups endpoint to return logical groupings of data items. Currently returns 501 Not Implemented.

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Proposed solution

1. Data groups provide a way to logically group related data items, separate from categories:

   • Groups can span multiple categories
   • Groups are defined by namespace hierarchy or explicit configuration

2. Auto-generate groups based on:

   • Topic namespace structure (e.g., /robot/arm/ → "arm" group)
   • Explicit groupings in manifest file
   • Message field groupings for complex types

3. Response format:

{
  "items": [
    {
      "id": "motion",
      "name": "Motion Data",
      "description": "Position, velocity, and acceleration data",
      "dataIds": ["position", "velocity", "acceleration"]
    },
    {
      "id": "environment",
      "name": "Environmental Sensors",
      "description": "Environmental measurement data",
      "dataIds": ["temperature", "humidity", "pressure"]
    }
  ]
}

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Additional context

• Route already registered in rest_server.cpp, needs handler implementation
• Groups differ from categories: categories are semantic types, groups are logical collections
• Consider supporting nested groups for complex systems