feat: add initial schema migration for fresh database installs

- Create Migration_Initial_Schema that loads database.sql only on empty databases
- Existing installations skip this migration (tables already exist)
- Prevents duplicate column errors when migrations run on pre-populated schema
- Remove database.sql preloading from CI workflow - migrations handle schema setup

.github/workflows/build-release.yml

@@ -179,9 +179,6 @@ jobs:
             exit 1
           }
 
-      - name: Initialize database
-        run: docker exec -i mysql mysql -u root -proot ospos < app/Database/database.sql
-
       - name: Run PHPUnit tests
         env:
           CI_ENVIRONMENT: testing