fix(db): explicit TypeORM column types for nullable string/uuid columns

`string | null` / `uuid | null` columns reflect as Object and crash the
backend at metadata build (DataTypeNotSupportedError). Declare explicit
`type` on users.phone/email and cluster_allocation_logs FK id columns.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/clusters/entities/cluster-allocation-log.entity.ts

@@ -17,7 +17,9 @@ export class ClusterAllocationLog {
   @PrimaryGeneratedColumn('uuid')
   id: string;
 
-  @Column({ nullable: true })
+  // Explicit `type` required: `string | null` reflects as Object and crashes
+  // TypeORM at metadata build (DataTypeNotSupportedError).
+  @Column({ type: 'uuid', nullable: true })
   applicationId?: string | null;
 
   @ManyToOne(() => Application, { nullable: true, onDelete: 'SET NULL' })
@@ -27,14 +29,14 @@ export class ClusterAllocationLog {
   @Column()
   userId: string;
 
-  @Column({ nullable: true })
+  @Column({ type: 'uuid', nullable: true })
   poolId?: string | null;
 
   @ManyToOne(() => ClusterPool, { nullable: true, onDelete: 'SET NULL' })
   @JoinColumn({ name: 'poolId' })
   pool: ClusterPool;
 
-  @Column({ nullable: true })
+  @Column({ type: 'uuid', nullable: true })
   selectedClusterId?: string | null;
 
   @ManyToOne(() => Cluster, { nullable: true, onDelete: 'SET NULL' })