Add Mistral and DeepSeek bot detection to ai-bot-monitor

[jasperf]

Summary

Expands scripts/monitoring/ai-bot-monitor.sh to detect three previously untracked AI crawlers:

• MistralAI-User — Mistral's live Le Chat fetcher
• MistralAI-Index — Mistral's indexing crawler
• DeepSeekBot — DeepSeek's web crawler

All three are added to both the AI_BOTS display array and the aggregate AI_PATTERN matcher, so they now show up in per-bot request/bandwidth counts, scraped-page lists, and robots.txt compliance checks.

Why

Verified against ~2 months of production access logs across two WordPress sites:

• DeepSeekBot was actively crawling — real page fetches plus probes for /.env.production and framework build manifests — but went completely uncounted because the script never matched it.
• Neither Mistral bot has appeared at all (Mistral appears to rely on Common Crawl rather than running its own broad crawl), so reports were silently blind to whether it ever does.

Changes

• scripts/monitoring/ai-bot-monitor.sh — add the three UA patterns to AI_BOTS + AI_PATTERN
• CHANGELOG.md — [2.15.0] - 2026-06-26

Test

• bash -n scripts/monitoring/ai-bot-monitor.sh passes (no syntax errors)