[ENHANCEMENT] Add Request ID Middleware and Structured Error Handling

[Lochit-Vinay]

[Enhancement] Add request ID middleware and improve error responses

Closes #409

What I did

• Added a middleware to attach a unique request ID (X-Request-ID) to every request/response

• Implemented global exception handlers for:

  • HTTP errors
  • validation errors (422)
  • unexpected server errors

• Standardized error response format across the API

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Why this change

While testing the API, I noticed:

• error responses were inconsistent
• validation errors from FastAPI were a bit hard to read
• there was no easy way to trace requests during debugging

This change makes debugging easier and responses more consistent for API consumers.

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Example

Request (invalid input)

{
  "template_id": null,
  "input_text": ""
}

Response

{
  "error": {
    "type": "ValidationError",
    "message": "Invalid request data",
    "details": [
      {
        "field": "template_id",
        "issue": "Input should be a valid integer"
      },
      {
        "field": "input_text",
        "issue": "Input text cannot be empty"
      }
    ]
  }
}

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How I tested

• Ran the server locally using uvicorn api.main:app --reload
• Verified endpoints via /docs
• Sent invalid requests and confirmed structured 422 responses
• Checked that X-Request-ID header is present in responses

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Files changed

• api/main.py

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Notes

• No breaking changes
• Existing routes continue to work as before

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