feat: Implement OAuth2 authentication with Google and GitHub

- Added OAuth2 endpoints for Google and GitHub authentication.
- Created OAuth service to handle provider interactions and user info retrieval.
- Implemented user OAuth repository for managing user OAuth links in the database.
- Updated auth service to support linking existing users and creating new users via OAuth.
- Added CORS middleware to allow frontend access.
- Created tests for OAuth endpoints and service functionality.
- Introduced environment configuration for OAuth client IDs and secrets.
- Added logging for OAuth operations and error handling.

uv.lock

@@ -46,6 +46,7 @@ dependencies = [
     { name = "bcrypt" },
     { name = "email-validator" },
     { name = "fastapi", extra = ["standard"] },
+    { name = "httpx" },
     { name = "pydantic-settings" },
     { name = "pyjwt" },
     { name = "sqlmodel" },
@@ -69,6 +70,7 @@ requires-dist = [
     { name = "bcrypt", specifier = "==4.3.0" },
     { name = "email-validator", specifier = "==2.2.0" },
     { name = "fastapi", extras = ["standard"], specifier = "==0.116.1" },
+    { name = "httpx", specifier = "==0.28.1" },
     { name = "pydantic-settings", specifier = "==2.10.1" },
     { name = "pyjwt", specifier = "==2.10.1" },
     { name = "sqlmodel", specifier = "==0.0.24" },