Update use cases hub with real client scenarios

[puleri]

Summary

• replaced placeholder use case entries on /use-cases with concrete real-world scenarios
• added the three requested highlights:
  • WordPress to Next.js migration that improved web scores and lead conversion while preserving trusted UX
  • cybersecurity SaaS sales pipeline optimization using Salesforce data organized via Snowflake API dashboards
  • startup outage response with a focused codebase audit after a valuation-critical incident
• updated featured use case cards to mirror the same real scenarios
• aligned filter options with the updated business types and challenge categories

Testing

• not run (content/data update only)

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Codex Task