[BE-40] Add Stale Jobs Detector for surfacing stuck async processing tasks

[devwums]

Problem

@nestjs/schedule is installed but never used. Documents can get stuck in processing states if async jobs silently fail, and there is no scheduled task to surface or resolve them.

Proposed Solution

Create backend/cntr/stale-jobs-detector.job.ts exporting StaleJobEntry interface ({ entityId: string, entityType: 'BOOKING' | 'PAYMENT', status: string, stuckSinceHours: number }), and detectStaleJobs(entities: Array<{ id: string, type: string, status: string, updatedAt: Date }>, staleThresholdHours = 2, now?: Date): StaleJobEntry[]. Returns entries stuck in non-terminal statuses for longer than the threshold. All implementation must live inside backend/cntr/.

Acceptance Criteria

• File at backend/cntr/stale-jobs-detector.job.ts
• Non-terminal statuses treated as potentially stale: PENDING, PROCESSING, ANALYZING
• stuckSinceHours computed from now - updatedAt
• Completed/cancelled statuses are never returned
• Accepts optional now: Date for testability
• Unit test at backend/cntr/stale-jobs-detector.job.spec.ts

[barry01-hash]

My chief, i will love to work on this issue

[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue

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[nanaf6203-bit]

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can I please take this issue please?

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[grantfox-oss]

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[grantfox-oss]

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@nanaf6203-bit's PR #1313 was approved and merged by @yusuftomilola.

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