fix(compression): restore sane defaults and cap summary at 12K tokens

- threshold: 0.80 → 0.50 (compress at 50%, not 80%)
- target_ratio: 0.40 → 0.20, now relative to threshold not total context
  (20% of 50% = 10% of context as tail budget)
- summary ceiling: 32K → 12K (Gemini can't output more than ~12K)
- Updated DEFAULT_CONFIG, config display, example config, and tests

run_agent.py

@@ -1009,10 +1009,10 @@ class AIAgent:
         _compression_cfg = _agent_cfg.get("compression", {})
         if not isinstance(_compression_cfg, dict):
             _compression_cfg = {}
-        compression_threshold = float(_compression_cfg.get("threshold", 0.80))
+        compression_threshold = float(_compression_cfg.get("threshold", 0.50))
         compression_enabled = str(_compression_cfg.get("enabled", True)).lower() in ("true", "1", "yes")
         compression_summary_model = _compression_cfg.get("summary_model") or None
-        compression_target_ratio = float(_compression_cfg.get("target_ratio", 0.40))
+        compression_target_ratio = float(_compression_cfg.get("target_ratio", 0.20))
         compression_protect_last = int(_compression_cfg.get("protect_last_n", 20))
 
         # Read explicit context_length override from model config