⚡ Bolt: O(1) Hash Map index lookups for MemStorage

[Pmaster-dev]

💡 What: Introduced secondary index maps (usersByUsername, usersByExternalId, reputationsByUserId) in server/storage.ts.

🎯 Why: High-frequency storage lookups (getUserByUsername, getUserByExternalId, getReputation) previously used Array.from(...).find(...), resulting in O(N) linear scans and heap array allocations on every request.

📊 Impact: Reduces time complexity from O(N) to O(1) constant time lookups and eliminates heap array allocation per query. Benchmark of 50,000 lookups completed in ~16ms (~0.32 μs/op).

🔬 Measurement: Verified with benchmark across 1,000 user/reputation records.

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PR created automatically by Jules for task 10423314552494981883 started by @Pmaster-dev

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