feat(backend): implement global search api

[a7hu-15]

Description

This PR introduces a Global Search API to the backend, allowing the frontend to search across different entities (Users and Projects) through a single endpoint.

Summary of changes:

• Search Router (backend/app/routers/search.py): Added a /search/ GET endpoint that accepts a query string q.
• Search Logic (backend/app/services/search_service.py): Implemented fuzzy search (ilike) using SQLAlchemy to match the query against:
  • Users: username, first name, last name, and headline.
  • Projects: title, description, and tagline.
• Schemas (backend/app/schemas/search.py): Created SearchResult models to return a unified payload.

How it Works (Example Usage)

Here is an example of what the new API returns when a user searches for a query like q=react:

GET /api/search/?q=react

{
  "users": [
    {
      "id": "123e4567-e89b-12d3-a456-426614174000",
      "username": "react_developer_99",
      "first_name": "John",
      "last_name": "Doe",
      "headline": "Frontend Engineer | React Enthusiast"
    }
  ],
  "projects": [
    {
      "id": "987fcdeb-51a2-43d7-9012-426614174000",
      "title": "React Dashboard Setup",
      "description": "An open source admin dashboard built with React and Tailwind.",
      "tagline": "Modern React Admin"
    }
  ]
}

(Note: As this is a backend API implementation, there are no frontend UI changes to screenshot yet. The above JSON demonstrates the API behavior.)

Related Issue

No linked issue.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Added pytest configurations in backend/tests/conftest.py using fastapi.testclient.TestClient.
• Created unit tests in backend/tests/test_search.py to verify the search endpoint handles queries correctly and returns the expected structured data.

[nensii21]

Thanks for opening this PR. The description is currently incomplete. Please update it with:

A clear summary of the changes made.
The issue number this PR addresses (e.g. Closes #123).
The type of change.
How you tested the implementation.
Attached video and screenshots of what changes you have made

Once the PR description is updated, I'll proceed with the review.