chore: refresh Agent Threat Rules galaxy 336 -> 713 rules (ATR 3.5.6)

[eeee2345]

What

Refreshes the Agent Threat Rules galaxy from 336 → 713 cluster values (ATR 2.0.12 → 3.5.6), regenerated with this repo's own scripts/generate-atr-galaxy.py.

• clusters/agent-threat-rules.json: 336 → 713 values
• galaxies/agent-threat-rules.json: version 1 → 2, description count updated
• scripts/generate-atr-galaxy.py: hardcoded "336 rules" description → 713, version 1 → 2

Why

The ATR cluster is pinned at an early ATR release (336 rules); ATR is now at 3.5.6 with 713 published detection rules covering the same 9 attack classes (prompt injection, tool poisoning, context exfiltration, agent manipulation, etc.).

How

Ran python3 scripts/generate-atr-galaxy.py --rules-dir <agent-threat-rules/rules @ 3.5.6>. Because the script derives cluster-value UUIDs deterministically (UUID5), every existing rule keeps its UUID — this is purely additive plus the metadata bump. The run also refreshed 1,311 MITRE ATLAS + ATT&CK relationships across 712 rules from the current mitre-* clusters.

Validation

• clusters/agent-threat-rules.json and galaxies/agent-threat-rules.json validate against schema_clusters.json / schema_galaxies.json
• 713 cluster values, all UUIDs unique
• Files normalised with jq --sort-keys (so validate_all.sh produces no diff)