llms.txt is missing the 6 most recently added explainers

[yakew7]

Where: llms.txt (root), ## Explainers section.

llms-full.txt (the full-text companion file, regenerated and CI-checked by scripts/build_explainers.py/check_generated_files_current.py) correctly includes all 53 current explainers. llms.txt - the short index file, maintained separately - is missing the 6 newest ones entirely:

• accuracy-equality
• bootstrap-confidence-intervals
• mitigation-strategies
• fairness-through-unawareness
• lime
• counterfactual-explanation

Repro: grep -c "accuracy-equality\|bootstrap-confidence-intervals\|mitigation-strategies\|fairness-through-unawareness\|lime.html\|counterfactual-explanation" llms.txt returns 0.

Why it matters: llms.txt is the short index AI answer engines/crawlers are pointed at first (per the llmstxt.org convention this repo's own llms-full.txt header cites) - six real, published explainers are currently invisible to anything that only reads the index and not the full-text file.

Suggested fix: add the 6 missing - [Title](https://www.thefaircode.xyz/explainers/<slug>.html) lines to llms.txt's ## Explainers section, matching the existing entries' format. Since llms.txt isn't covered by scripts/check_generated_files_current.py's TEXT_GLOBS (only llms-full.txt is), this file can drift silently again - worth adding it to that check, or to scripts/build_explainers.py's own output, in the same PR.