feat: implement core infrastructure for service graph visualization with custom nodes, layout components, and UI state management.

[KOUSHIKG04]

Summary

• New Features

  • Added support for database nodes in the graph editor alongside service nodes.
  • Introduced workspace panel organization for better layout management.
  • Implemented light/dark theme toggle with persistent preferences.

• UI/Style

  • Updated top bar branding and visual design.
  • Improved responsive design for mobile devices.
  • Enhanced theme-aware styling across components.

• Documentation

  • Restructured README with expanded setup instructions and validation guidelines.
  • Added comprehensive "Key Decisions" and updated "Known Limitations" sections.