Add verification claim funnel observability metrics and dashboard docs

[Silver36-ship-it]

Closes #561

PR Description

Summary

Add Prometheus funnel observability for claim lifecycle transitions, including verification path coverage and dashboard-ready metric names.

What changed

• verification.service.ts

  • Injected MetricsService
  • Added funnel metric recording for verification transitions
  • Created recordClaimFunnelTransition() and claimStatusToFunnelStage()
  • Emits:
    • claim_funnel_total{stage="verified"}
    • claim_funnel_current{stage="verified"}

• verification.module.ts

  • Imported MetricsModule so VerificationService can consume MetricsService

• verification.service.spec.ts

  • Added MetricsService mock
  • Added assertions verifying funnel metrics are emitted when verification succeeds

• claims.service.ts

  • Existing claim lifecycle metric recording remains intact
  • Ensures created/approved/disbursed stages continue to emit funnel metrics

• metrics.service.ts

  • Confirmed dynamic counter/gauge helpers already support metric labels

• testnet-observability-dashboard.md

  • Documented dashboard-ready metrics:
    • claim_funnel_total{stage}
    • claim_funnel_current{stage}
  • Included supported stages:
    • created
    • verified
    • approved
    • disbursed

Validation

• Confirmed no diagnostics errors in modified backend files
• Verified branch ObservabilityMetricsForVerificationClaimFunnel created and pushed

Notes

• This change instruments the AI verification flow directly in VerificationService.processVerification()
• It avoids duplicate metric logic by using the same funnel stage naming conventions already used in ClaimsService
• It does not add files to the codebase outside the backend observability and verification implementation paths

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[Cedarich]

@Silver36-ship-it kindly fix workflow

[Cedarich]

Kindly remove changes from backend CI file

[Cedarich]

@Silver36-ship-it