chore: remove duplicate dependency-update workflow

[graycreate]

Summary

• Removed the custom dependency-update.yml workflow that duplicates Dependabot functionality
• Keeping only Dependabot for dependency management as it provides superior features

Why this change?

Both dependency-update.yml and Dependabot were scheduled to run weekly on Mondays at 9 AM for dependency checks. However:

Dependabot advantages:

• ✅ Automatically creates PRs when updates are found
• ✅ Groups related dependencies to reduce PR noise
• ✅ Handles multiple ecosystems (Gradle + GitHub Actions)
• ✅ Native GitHub feature with no custom code to maintain

Custom workflow limitations:

• ❌ Mainly generates reports, requires manual PR creation
• ❌ Only checks Gradle dependencies
• ❌ Requires custom scripts and maintenance
• ❌ No dependency grouping

Test plan

• Verified Dependabot configuration remains intact
• Dependabot will continue to run weekly as configured
• Monitor next week's Dependabot run to ensure it works as expected

🤖 Generated with Claude Code

[Copilot]

Pull Request Overview

Removes the custom dependency-update workflow in favor of using Dependabot’s built-in features for scheduled dependency management.

• Eliminates redundant dependency-update.yml file
• Consolidates dependency updates under Dependabot only