feat: Critical SSL connection stability improvements (v1.4.8)

- Enhanced SSL error reporting with detailed error codes and descriptions
- Added connection state validation before SSL operations
- Implemented automatic retry logic for transient SSL errors (SSL_ERROR_WANT_READ/WRITE)
- Added 5-second timeout protection for SSL read operations to prevent indefinite hangs
- Improved WebSocket frame transmission with retry mechanisms and partial write handling
- Applied improvements to all three C tools (wssshc, wsssh, wsscp)
- Updated CHANGELOG.md and TODO.md for version 1.4.8
- Fixed WebSocket frame sending failures that were causing connection drops
- Enhanced connection resilience with better error recovery

Technical Details:
- SSL error diagnostics using SSL_get_error() and ERR_error_string_n()
- Connection state validation using SSL_get_shutdown()
- Timeout protection using select() with 5-second timeout
- Retry logic with configurable limits (up to 3 attempts)
- Consistent error reporting across all SSL operations
- Backward compatible improvements that don't affect normal operation