Implement Milestone/Endgame Summary Screen

[adam4813]

Add a screen that summarizes player progress and celebrates important milestones or end-of-game achievements.

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UI Mockup/Wireframe (ASCII):

ENDGAME SUMMARY SCREEN
=======================
┌───────────────────────────────┐
│  Congratulations!             │
├───────────────────────────────┤
│  Stars: 5/5                   │
│  Tenants: 2,000               │
│  Income: $20,000/hr           │
│  Playtime: 3:12:44            │
│  Achievements Unlocked: 8     │
│  Challenges Completed: 3      │
│  Best Moments:                │
│   - 1,000 tenants in 12 days  │
│   - 100 floors built          │
└───────────────────────────────┘
│ [Restart] [Main Menu]         │
└───────────────────────────────┘

Tasks:

• Show summary screen after game completion or major milestone
• Display stats: stars, tenants, income, playtime, achievements, best moments
• Option to restart, continue, or return to main menu
• Save summary for viewing later

Acceptance Criteria:

• Endgame/milestone summary is shown at correct times
• All relevant stats and achievements are summarized
• Options to restart/main menu function
• Matches ASCII mockup