⚡ Bolt: Optimize checkAchievements database operations

[google-labs-jules]

⚡ Bolt Optimization: checkAchievements

💡 What:
Optimized the checkAchievements function in gamificationController.js.
Instead of executing database inserts and user updates sequentially inside the achievement loop, I:

1. Accumulated the total XP reward.
2. Collected all insert promises (user_achievements, notifications, tracking).
3. Executed all inserts concurrently using Promise.all.
4. Called User.addXP once with the total accumulated XP.

🎯 Why:
The original implementation suffered from an N+1 query problem (actually N*4) when multiple achievements were unlocked simultaneously. Each achievement triggered 3 separate DB writes plus 1 read/write for user update.
For 3 achievements, this meant ~12 sequential DB operations.
The new implementation reduces this to ~2 sequential steps (Batch Inserts + 1 User Update).

📊 Impact:

• Reduces users table updates from N to 1.
• Parallelizes N inserts for auxiliary tables.
• Significantly reduces latency for users unlocking multiple achievements (e.g., leveling up or completing complex quests).

🔬 Measurement:
Added backend/tests/gamificationPerformance.test.js which verifies that User.addXP is called exactly once with the total XP amount, confirming the optimization.

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PR created automatically by Jules for task 3281644593256344958 started by @4444J99

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[4444J99]

Engaging as a real, still-open perf want (not falsely marked done): I confirmed the N+1 on current main — gamificationController.checkAchievements loops over unlocked achievements and runs 3 sequential awaits per achievement (INSERT user_achievements, user.addXP → user.save, INSERT notifications, around lines 133–173). The safe distilled form is to aggregate XP into a single addXP and bulk-insert the achievement + notification rows once. I'm not blind-merging this stale/conflicting draft because a DB-write refactor needs a live-DB integration test to verify correctness (achievement unlocking must not regress). Keeping this open as the anchor for that verified distillation — never closed.