docs: Replace WSL guide with cross-platform development guide

Abandoned WSL approach due to additional overhead and performance issues
with Windows filesystem access. Instead, documented clear guidelines for
switching between Windows 11 (primary) and Linux (secondary) development
environments.

Changes:
- Removed WSL_LINUX_SETUP_GUIDE.md (overly complex for needs)
- Added CROSS_PLATFORM_DEV_GUIDE.md with:
  * Complete Windows 11 setup (primary dev environment)
  * Complete Linux setup (cloud/deployment environment)
  * Cross-platform code guidelines (pathlib, line endings, etc.)
  * Environment switching strategies
  * Common issues and solutions
  * Testing and CI/CD examples
- Updated README.md Platform Support section
- Emphasizes Windows 11 as recommended development platform

Rationale:
WSL adds unnecessary overhead when Windows environment works perfectly.
Cross-platform compatibility achieved through proper path handling
(pathlib) and configuration management, not environment duplication.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: michshat