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/modules/schedules/schedules.service.ts

@@ -41,8 +41,7 @@ export class SchedulesService {
       cron_expression: dto.cron_expression,
       timezone: timezone,
       task_config: dto.task_config || {},
-      is_enabled: true,
-      last_run: null,
+      is_active: true,
       next_run: null, // Would be calculated by scheduler
       created_at: new Date(),
     });
@@ -114,7 +113,7 @@ export class SchedulesService {
       throw new NotFoundException(`Scheduled task ${taskId} not found`);
     }
 
-    task.is_enabled = enabled;
+    task.is_active = enabled;
     const updated = await this.taskRepository.save(task);
 
     // TODO: Enable/disable task in scheduler