fix: Align NestJS entities with actual DB schema — 12 files, 5 entities

Root cause of all remaining 500s: TypeORM entities were scaffolded with
"ideal" column names that don't match the Postgres columns created by
the Rust migrations. Every query generated SQL referencing non-existent
columns.

Entity fixes:
- notifications_config: email_enabled→email_alerts_enabled, removed
  6 phantom columns (email_address, notify_on_start, notify_on_stop,
  notify_on_player_threshold, player_threshold), renamed 4 notify
  columns to match DB (notify_server_crash, notify_wipe_start, etc),
  added 3 missing columns (notify_server_offline, notify_store_purchase,
  notify_player_report)
- team_members: joined_at→accepted_at (nullable, matches DB)
- roles: removed description column (doesn't exist in DB)
- scheduled_tasks: is_enabled→is_active, removed phantom last_run
- wipe_profiles: pre/post_wipe_config nullable→NOT NULL with default

Service/DTO fixes:
- Updated all property references across notifications, team, schedules
  services and DTOs to match corrected entity names
- Added is_active to UpdateTaskDto (frontend sends it, was being
  rejected by forbidNonWhitelisted validation)
- Removed description from CreateRoleDto

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-nest/src/entities/role.entity.ts

@@ -12,9 +12,6 @@ export class Role {
   @Column({ type: 'varchar', length: 50 })
   role_name: string;
 
-  @Column({ type: 'text', nullable: true })
-  description: string | null;
-
   @Column({ type: 'boolean', default: false })
   is_system_default: boolean;