feat: enhance authentication and publication download tracking

- Added JWT authentication support with configurable secret and expiration.
- Introduced optional API key validation for endpoints.
- Implemented tracking of publication downloads by researchers, storing records in a new PublicationDownload model.
- Updated export endpoints to conditionally register downloads based on user authentication.
- Enhanced researcher search response to indicate if publications were downloaded by the current user.
- Updated environment configuration to include new JWT settings.

backend/app/schema/auth.py

@@ -0,0 +1,12 @@
+from pydantic import BaseModel, Field
+
+
+class OrcidLoginRequestSchema(BaseModel):
+    # `code` is the authorization code returned by ORCID OAuth after the user signs in.
+    # Exchanging it for tokens must happen server-side.
+    code: str = Field(..., examples=["Q70Y3A"])
+
+
+class OrcidLoginResponseSchema(BaseModel):
+    access_token: str
+    token_type: str = "bearer"