Refactor: deplacer backend dans apps/backend

apps/backend/app/models/project_skill.py

@@ -0,0 +1,22 @@
+from sqlalchemy import Table, Column, Integer, ForeignKey
+
+from app.database import Base
+
+project_skills = Table(
+    "project_skills",
+    Base.metadata,
+
+    Column(
+        "project_id",
+        Integer,
+        ForeignKey("projects.id", ondelete="CASCADE"),
+        primary_key=True
+    ),
+
+    Column(
+        "skill_id",
+        Integer,
+        ForeignKey("skills.id", ondelete="CASCADE"),
+        primary_key=True
+    )
+)