docs: Add TROUBLESHOOTING.md guide for common development issues (#7738)

## Summary

Adds a comprehensive `TROUBLESHOOTING.md` guide to help developers
resolve common development issues.

## Motivation

a developer reported issues where `pnpm dev` would get stuck on 'nx
serve'. This highlighted the need for centralized troubleshooting
documentation to help developers quickly resolve common issues without
having to wait for help.

## Changes

- Created `TROUBLESHOOTING.md` with FAQ-style documentation
- Added Mermaid flowchart for quick issue diagnosis
- Documented solutions for common problems:
  - Development server issues (nx serve hanging)
  - Build and TypeScript errors
  - Dependency and package management problems
  - Testing issues
  - Git and branch conflicts

## Structure

The guide includes:
- Quick diagnostic flowchart (Mermaid)
- Frequently Asked Questions with:
  - Clear symptoms
  - Step-by-step solutions
  - Explanations of why issues occur
- Links to community support resources
- Contribution guidelines

## Test Plan

- [x] File created and committed
- [x] Mermaid flowchart renders correctly
- [x] All commands are accurate and tested
- [x] Links to Discord and GitHub are valid

🤖 Generated with [Claude Code](https://claude.com/claude-code)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7738-docs-Add-TROUBLESHOOTING-md-guide-for-common-development-issues-2d26d73d365081eda291e619b3067bc6)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: snomiao <snomiao@gmail.com>
Co-authored-by: GitHub Action <action@github.com>

browser_tests/README.md

@@ -27,7 +27,7 @@ cp -r tools/devtools/* /path/to/your/ComfyUI/custom_nodes/ComfyUI_devtools/
 
 ### Node.js & Playwright Prerequisites
 
-Ensure you have the Node.js version from `.nvmrc` installed (currently v24).
+Ensure you have the Node.js version specified in `.nvmrc` installed.
 Then, set up the Chromium test driver:
 
 ```bash