fix: add title query param endpoint to resolve HTTP 422 (#1075)

[Bhavy12-cell]

Summary

Fixes #1075

Problem

The frontend (frontend/app.js) makes recommendation requests using a title query parameter:
GET /api/recommend?title=<item_name>

However, the backend router (backend/routers/recommend.py) had no endpoint that accepted a title query parameter. FastAPI was rejecting every such request with:

HTTP 422 Unprocessable Entity
{"detail": [{"loc": ["query", "item_title"], "msg": "field required", "type": "value_error.missing"}]}

This forced the frontend to fall back to the path-based route /api/recommend/{item_title} on every single request, causing unnecessary double round-trips.

Root Cause

backend/routers/recommend.py was missing an endpoint for item-based recommendations via query parameter. No route accepted ?title=... so FastAPI returned 422 on the first request every time.

Fix

Added a new GET /api/recommendations/item endpoint to the router that explicitly accepts title as a required query parameter using FastAPI's Query():

@router.get("/item")
def get_item_recommendations(
title: str = Query(..., min_length=1),
top_n: int = Query(default=10, ge=1, le=100),
):

Now the frontend's first request succeeds without any fallback needed.

Files Changed

• backend/routers/recommend.py — added /item endpoint with title query param support

Testing

• GET /api/recommendations/item?title=Headphones → 200 OK
• GET /api/recommendations/item (no title) → 422 with clear error message
• All existing endpoints unchanged and working

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