test: Increase coverage >70% and fix test config

[albertoivo]

• Fixed vitest configuration to load environment variables from .env, resolving "Erro de Configuração" in tests.
• Fixed firestore.test.ts by updating getDoc mock to return a default object with exists() method, resolving a TypeError.
• Created new unit tests for MissionList, PowerUpBar, LevelBadge, Mascot, and Header components.
• Increased overall test coverage significantly (Gamification components from ~0% to >85%).
• Verified all tests pass.

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PR created automatically by Jules for task 10939491156008589899 started by @albertoivo

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