add file and folder_zip svg icons

apps/backend/app/models/project_skill.py

@@ -10,13 +10,15 @@ project_skills = Table(
         "project_id",
         Integer,
         ForeignKey("projects.id", ondelete="CASCADE"),
-        primary_key=True
+        primary_key=True,
+        nullable=False
     ),
 
     Column(
         "skill_id",
         Integer,
         ForeignKey("skills.id", ondelete="CASCADE"),
-        primary_key=True
+        primary_key=True,
+        nullable=False
     )
 )