⚡ Bolt: Combine SQLite COUNT aggregations in learning_report.py

[thebearwithabite]

💡 What: Refactored generate_report in learning_report.py to combine three sequential SELECT COUNT(*) queries on the learning_events table into a single query using conditional aggregation (COUNT(CASE WHEN ...)).
🎯 Why: Multiple sequential aggregations on the same table cause redundant full table or index scans (an N+1 problem for table reads), reducing I/O throughput. Combining them into a single query requires only one pass over the data.
📊 Impact: Reduces database reads for the learning events base metrics by 66% (from 3 table scans to 1). The actual measurable impact will scale proportionally with the size of the learning_events table.
🔬 Measurement: Verify visually via the output of generate_report that the Knowledge Base Stats continue to produce the correct counts, or by isolating the SQL logic in a mock execution.

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PR created automatically by Jules for task 102955351666156684 started by @thebearwithabite

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