⚡ Bolt: optimize SessionManager initialization and queries

[charles-forsyth]

💡 What:

Optimized the SessionManager class to reduce database overhead and resolve an N+1 query problem in the session listing logic.

🎯 Why:

• list_sessions was performing a separate query for every running child session to check its parent's status.
• Multiple individual UPDATE and commit() calls were being made in a loop for crashed sessions.
• _init_db (including migrations and PRAGMAs) was running every time a SessionManager was instantiated, which happens frequently in recursive research.
• Missing indexes were slowing down sorting and filtering by interaction_id, parent_id, and updated_at.

📊 Impact:

• Reduces list_sessions query count from O(N) to O(1) for fetching session data.
• Reduces list_sessions update count from O(M) to O(1) for marking crashed sessions.
• Eliminates redundant database initialization overhead in the same process (average ~0.5ms saved per instantiation).
• Improves lookup and sorting performance as the database grows via new indexes.

🔬 Measurement:

Verified using tests/test_performance.py, which uses a proxy connection to count exact database queries. Results:

• list_sessions query count for 5 child sessions: 6 -> 1
• list_sessions update count for 5 crashed sessions: 5 -> 1
• Redundant init queries: 3+ -> 0
• All 33 tests passed in the full suite.

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PR created automatically by Jules for task 5935941829814978723 started by @charles-forsyth

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