docs: add Docker Compose dev setup and local development guide

[harmeshgv]

Summary

Adds a developer-friendly local development setup including:

• docker-compose.dev.yml with clean defaults
• .env.example with documented required variables
• docs/guides/local-development.md step-by-step guide

Improves onboarding by making the full local stack reproducible and beginner-friendly. ISSUE NO #3

Changes

• Added docker-compose.dev.yml with proper service order:

  • anvil → deploy → node + bridge

• Added .env.example with documented environment variables

  • Clarified that BRIDGE_API_TOKEN is mandatory for Bridge startup

• Added docs/guides/local-development.md with:

  • Prerequisites
  • Setup instructions
  • Startup flow explanation
  • Service ports
  • Common issues
  • Clean restart test section

Test Plan

• Unit tests pass (make test)
• Lint passes (make lint)
• Relevant new tests added

Checklist

• Code follows project conventions
• No secrets or credentials included
• Documentation updated if needed