fix(ci): add required env vars to lint-backend workflow

Mypy needs to import app modules during analysis, which requires valid
Settings configuration. Added dummy env vars for:
- PROJECT_NAME, FIRST_SUPERUSER (required fields)
- DATABASE_URL with postgresql+psycopg:// scheme for psycopg v3
- All Supabase and Redis config values

This matches the pattern used in test-backend.yml and generate-client.yml
workflows.

Related to CUR-29

🤖 Generated by Aygentic

Co-Authored-By: Aygentic <noreply@aygentic.com>

Author: amostt

.github/workflows/lint-backend.yml

@@ -30,3 +30,17 @@ jobs:
       - name: Run linters
         run: uv run bash scripts/lint.sh
         working-directory: backend
+        env:
+          # Required env vars for Settings class initialization during mypy analysis
+          PROJECT_NAME: CurriculumExtractor
+          SECRET_KEY: just-for-linting
+          FIRST_SUPERUSER: admin@example.com
+          FIRST_SUPERUSER_PASSWORD: just-for-linting
+          DATABASE_URL: postgresql+psycopg://postgres:password@localhost:5432/app
+          SUPABASE_URL: https://dummy.supabase.co
+          SUPABASE_ANON_KEY: dummy-anon-key
+          SUPABASE_SERVICE_KEY: dummy-service-key
+          REDIS_PASSWORD: dummy-redis-password
+          REDIS_URL: redis://:dummy@localhost:6379/0
+          CELERY_BROKER_URL: redis://:dummy@localhost:6379/0
+          CELERY_RESULT_BACKEND: redis://:dummy@localhost:6379/0