fix: resolve all issues assigned to Mercy60 (#364, #365, #375, #376)

[mercy60]

Closes #364, Closes #365, Closes #375, Closes #376

Changes

#364 — Refactor: split task orchestration from business logic

• Created tasks/task-orchestrator.service.ts with scheduling, retry (exponential backoff + jitter), queue management, and execution history
• Added maxRetries property to TaskEntity
• Updated TaskModule to register orchestrator

#365 — Bug: submission attachment scanning

• Added validateAttachment() with size/type/content-policy checks to SubmissionsService
• Added scanContentPolicy() and validateAttachment() to SecurityService
• Added contentPolicyViolation notification to NotificationsService
• Added env config: MAX_ATTACHMENT_SIZE_BYTES, ALLOWED_ATTACHMENT_TYPES, ATTACHMENT_SCANNING_ENABLED
• Updated SubmissionsModule to import SecurityModule

#375 — Bug: health checks miss dependency health

• Created health/health.service.ts checking Redis and Database health (ok/degraded/unavailable)
• Added isHealthy() to RedisService and DatabaseService
• Updated HealthController to use HealthService for dependency-aware checks

#376 — Enhancement: readiness probes

• Created health/health.module.ts
• Added GET /health/ready and GET /health/live endpoints
• Added isReady(), getQueueDepth(), getLastHeartbeat(), heartbeat() to JobsService
• Registered HealthModule in AppModule
• Added READINESS_PROBE_TIMEOUT_MS env config

Bug fixes

• Fixed missing closing brace in redis.service.ts
• Fixed broken submissions.service.ts (duplicate class declarations merged)
• Fixed broken notifications.service.ts (duplicate imports, malformed constructor, missing closing braces)
• Fixed config.module.ts (missing Joi import, wrong schema export name validationSchema → contractEnvSchema, dead inline schema now properly merged via .concat())
• Removed duplicate export class AppModule {}

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@mercy60 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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[MaryammAli]

LGTM