feat: read prompt caching cache_ttl from config

- Load prompt_caching.cache_ttl in AIAgent (5m default, 1h opt-in)
- Document DEFAULT_CONFIG and developer guide example
- Add unit tests for default, 1h, and invalid TTL fallback

Made-with: Cursor

hermes_cli/config.py

@@ -521,6 +521,12 @@ DEFAULT_CONFIG = {
 
     },
 
+    # Anthropic prompt caching (Claude via OpenRouter or native Anthropic API).
+    # cache_ttl must be "5m" or "1h" (Anthropic-supported tiers); other values are ignored.
+    "prompt_caching": {
+        "cache_ttl": "5m",
+    },
+
     # AWS Bedrock provider configuration.
     # Only used when model.provider is "bedrock".
     "bedrock": {