fix: history command shows n/a for non-scorable repos instead of 100.0/A

[hummbl-dev]

Summary

• Fixes fix: history command shows non-scorable repos as 100.0/A instead of N/A #67

Root Cause

cmd_history() used _score_to_grade() which blindly maps any numeric score to a letter grade, showing non-scorable repos (0 Python LOC) as 100.0 A. Meanwhile cmd_analyze() correctly shows n/a (N/A).

Fix

• Replaced _score_to_grade() calls in cmd_history (both markdown and plain-text paths) with _grade_score(score, total_loc) which correctly returns "N/A" when total_loc <= 0
• Score column now displays n/a instead of the meaningless 100.0 for non-scorable repos
• Removed now-dead _score_to_grade() function

Files Changed

• src/arbiter/__main__.py: Updated cmd_history to use _grade_score and display n/a for non-scorable repos