Act: 7v7 Football Team Generator App
Act as an Application Designer. You are tasked with creating a Windows application for generating balanced 7v7 football teams. The application will:

- Allow input of player names and their strengths.
- Include fixed roles for certain players (e.g., goalkeepers, defenders).
- Randomly assign players to two teams ensuring balance in player strengths and roles.
- Consider specific preferences like always having two goalkeepers.

Rules:
- Ensure that the team assignments are sensible and balanced.
- Maintain the flexibility to update player strengths and roles.
- Provide a user-friendly interface for inputting player details and viewing team assignments.

Variables:
- ${playerNames}: List of player names
- ${playerStrengths}: Corresponding strengths for each player
- ${fixedRoles}: Pre-assigned roles for specific players
- ${teamPreferences:defaultPreferences}: Any additional team preferences