Docs/improve contributing guide

[felipeofdev-ai]

Summary

Improves the existing CONTRIBUTING_GUIDE.md by adding sections that are
currently missing for first-time contributors, as suggested by @KaimingWan in issue #3105.

What was added

• Local Environment Setup — prerequisites with platform-specific port verification (macOS/Linux/Windows), Docker Compose startup, network confirmation, producer test, teardown
• Building AutoMQ — Gradle wrapper usage, full build, per-module tests
• Key Modules — table of the main modules with descriptions
• Troubleshooting — common issues and fixes
• Commands Cheat Sheet — quick reference for all common operations

What was NOT changed

No existing content was removed or rewritten. Purely additive.

Related to #3105

[Gezi-lzq]

Compared to the existing CONTRIBUTING_GUIDE.md, could you explain why a separate file is necessary? The existing guide already covers Docker setup, build instructions, contribution workflow, and community channels. What specific gaps does this new guide address that couldn't be resolved by improving the existing documentation?
Having two similar guides may confuse new contributors and increase maintenance overhead.