refactor: move list_tools to utils and remove rename_readings script

[fshowalter]

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[claude]

Claude finished @fshowalter's task in 35s —— View job

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PR Review

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This is a clean, straightforward refactor. Here's my assessment:

What changed:

• Deleted booklog/exports/list_tools.py (26 lines) — moved to booklog/utils/list_tools.py
• Updated imports in reading_log.py and stats.py to use the new location
• Deleted scripts/rename_readings.py (124 lines) — a one-off migration script

Code quality: ✅

The consolidation makes sense. list_tools utilities (group_list_by_key, list_to_dict_by_key) are general-purpose and belong in utils/ rather than exports/. No callers of the old location remain — the import migration is complete and correct.

One minor observation: the deleted booklog/exports/list_tools.py contained list_to_dict_by_key in addition to group_list_by_key, but list_to_dict_by_key was not migrated to booklog/utils/list_tools.py. A quick grep confirms it has no remaining callers, so the removal is intentional and safe.

No issues found. This PR is a straightforward cleanup — net -152 lines with no regressions.