[REFACTOR] Centralize game logic and constants

[MrJacob12]

There is significant logic duplication across the codebase. Hardcoded values for pack
unlock requirements, income multipliers, and upgrade costs are defined in multiple
places (e.g., gameStore.ts and PackOpening.tsx). This makes the game difficult to
balance and prone to bugs.

Tasks:

• Create a centralized configuration file at src/config/gameConfig.ts.
• Extract pack requirements, upgrade cost formulas, and base multipliers into the
  config file.
• Implement a unified calculateCurrentIncome(state) helper function to be used for
  both offline and active income calculations.
• Refactor gameStore.ts and PackOpening.tsx to consume these shared constants and functions.