feat(sprint): 8.17 MiscellaneousCleanup

[samestrin]

Summary

Technical debt cleanup addressing 4 unrelated items: performance gaps, feature gaps, and test coverage issues.

Changes

• Storage Performance Optimization: Refactored SearchMemory to use batched processing with LIMIT/OFFSET and min-heap priority queue, reducing memory usage from O(n) to O(batch_size + topK)
• Markdown Chunker Enhancement: Added list hierarchy tracking to preserve parent list item context for code blocks inside nested lists
• HTML Chunker Test Coverage: Added comprehensive tests for fallbackToText error handling path (0% coverage issue)
• Memory Stats Query Optimization: Fixed N+1 query pattern by using LEFT JOIN to fetch Question/CreatedAt fields in single query

Files Changed

• 9 files modified (8 modified, 1 new)
• +688 insertions, -92 deletions
• New: storage_sqlite_bench_test.go (benchmark tests for large indexes)

Test Plan

• Code review passed (8/8 items verified)
• Sprint complete validation passed
• All SQLite tests passing
• Benchmarks show constant memory profile (~8840 B/op)
• Coverage maintained at 66%

Related

• Branch: feature/8.17_miscellaneous_cleanup
• Sprint: 8.17 - MiscellaneousCleanup
• Code Review: 2026-01-18_code-review.md