fix(db): declare onDelete on required FKs that had none

Eight required (nullable:false) FKs had no referential action. Set per the
codebase's existing pattern: CASCADE for owned relations (doctor_insurances,
doctor_secretaries), RESTRICT for owner/reference FKs (Doctor/Clinic.user_id,
invited_by_id, subscription plan/period). Only the two CASCADE FKs need DDL —
RESTRICT is the MySQL default.

src/Subscription/Entity/ClinicSubscription.php

@@ -27,11 +27,11 @@ class ClinicSubscription
     private int $entityId;
 
     #[ORM\ManyToOne(targetEntity: SubscriptionPlan::class)]
-    #[ORM\JoinColumn(nullable: false)]
+    #[ORM\JoinColumn(nullable: false, onDelete: 'RESTRICT')]
     private SubscriptionPlan $plan;
 
     #[ORM\ManyToOne(targetEntity: SubscriptionPeriod::class)]
-    #[ORM\JoinColumn(nullable: false)]
+    #[ORM\JoinColumn(nullable: false, onDelete: 'RESTRICT')]
     private SubscriptionPeriod $period;
 
     #[ORM\ManyToOne(targetEntity: Payment::class)]

src/Subscription/Entity/SubscriptionPeriod.php

@@ -19,7 +19,7 @@ class SubscriptionPeriod
     private string $uuid;
 
     #[ORM\ManyToOne(targetEntity: SubscriptionPlan::class, inversedBy: 'periods')]
-    #[ORM\JoinColumn(nullable: false)]
+    #[ORM\JoinColumn(nullable: false, onDelete: 'RESTRICT')]
     private SubscriptionPlan $plan;
 
     #[ORM\Column(type: 'string', length: 50)]