feat: Add referential routes for listing available plans and remove plans endpoint from admin routes

app/routes/referential.py

@@ -0,0 +1,17 @@
+"""Referential routes for reference data."""
+
+from flask import Blueprint
+
+bp = Blueprint("referential", __name__)
+
+
+@bp.route("/plans")
+def list_plans() -> dict:
+    """List all available plans."""
+    from app.models.plan import Plan
+    
+    plans = Plan.query.order_by(Plan.id).all()
+    return {
+        "plans": [plan.to_dict() for plan in plans],
+        "total": len(plans)
+    }