fix: Scale up infrastructure for Black Friday traffic surge

[hugorut]

Upgrading web_app instance to handle expected 10x traffic increase:

• Bump instance from m6g.4xlarge to c5.24xlarge for additional compute capacity
• Migrate EBS volume from io1 to gp3 for better price/performance ratio

Based on last year's metrics, we anticipate peak load of ~50k req/s during the Nov 24-27 weekend. The c5.24xlarge provides 96 vCPUs (vs previous 16) which should handle the increased load while maintaining p95 latency <100ms.

The gp3 migration reduces storage costs while maintaining required IOPS for our database workload.

Related: INFRA-1847

[github-actions]

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[infracost]

💰 Infracost report

Guardrails
❌ Costs increase by more than $12K/yr - approval required
	At least one project exceeded per-project threshold. Cost increased by $2,488, threshold was $1,000.
🔴 Costs increase by more than $6K/yr - warning only
	At least one project exceeded per-project threshold. Cost increased by $2,488, threshold was $200.

Monthly estimate increased by $2,488 📈

Changed project	Baseline cost	Usage cost*	Total change	New monthly cost
aws	+$2,488	+$0	+$2,488 (+908%)	$2,762

*Usage costs were estimated using Infracost Cloud settings, see docs for other options.

Estimate details

Key: * usage cost, ~ changed, + added, - removed

──────────────────────────────────
Project: aws
Module path: aws

~ aws_instance.my_web_app
  +$2,488 ($265 → $2,753)

    ~ Instance usage (Linux/UNIX, on-demand, m3.xlarge → c5.24xlarge)
      +$2,506 ($175 → $2,681)

    ~ root_block_device

        ~ Storage (general purpose SSD, gp2 → gp3)
          -$18 ($90 → $72)

Monthly cost change for aws (Module path: aws)
Amount:  +$2,488 ($274 → $2,762)
Percent: +908%

──────────────────────────────────
Key: * usage cost, ~ changed, + added, - removed

*Usage costs were estimated using Infracost Cloud settings, see docs for other options.

39 cloud resources were detected:
∙ 18 were estimated
∙ 21 were free

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_{This comment will be updated when code changes.}