Add achievements system with Discord UI and persistence

[Appurupai3]

Motivation

• Provide an in-app achievements catalogue and UI so players can view unlocked and progress achievements for economy games.
• Persist unlocked achievements to a scoreboard file so progress is stored across runs.

Description

• Add a new dcrbot/achievements.py that defines an Achievement dataclass, a large ACHIEVEMENTS catalogue, checks for many game-specific stats, functions to load/save records to leaderboard/info/achievements.json, and sync_user_achievement_records that writes newly unlocked achievements.
• Implement build_achievement_embed to generate Discord embeds for overall or per-game achievement views and add AchievementGameSelect and AchievementView UI components for selection and display.
• Wire the new feature into bot.py by importing AchievementView and build_achievement_embed and adding Achievement buttons to EconomyMenu and GameMenu that call open_account then send the achievement embed/view.

Testing

• No automated tests were executed for this change.

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Codex Task