Document limits, load control and performance

- New docs/09-limits-and-performance.md: principles, all protection
  layers, what players see, configuration reference, measurements,
  tuning guide, monitoring and how to test
- Server chapter summarises the limits and links to chapter 9; circuit
  breaker description and AI_MAX_INFLIGHT default corrected
- Architecture: new files in the layout, design decisions for load
  handling; docs index lists chapter 9
- Protocol, AI and operations chapters link to chapter 9; test counts
- Root and component READMEs describe the limits and settings

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

wizard_ai/README.md

@@ -16,12 +16,16 @@ provides everything around it.
   `Policy.update`, with checkpointing
 - `training/evaluate.py` — play agents against each other (mean score, win rate)
 - `service/client.py` — production: connects to `ws://wizard_server:8083/internal/ai`,
-  answers `decide` requests, reconnects automatically
+  answers `decide` requests, reconnects automatically. Work is bounded: `AI_WORKERS` (1)
+  parallel decisions, at most `AI_MAX_QUEUE` (64) requests in progress (more are answered
+  "overloaded"), expired requests are dropped, and from `AI_DEGRADE_QUEUE` (8) waiting requests —
+  or when the model is too slow — the heuristic decides instead of the model
+  (see `../docs/09-limits-and-performance.md`)
 
 ```bash
 pip install -r requirements-dev.txt
 python -m wizard_ai train --episodes 5000 --out models/latest
 python -m wizard_ai evaluate --agents model,heuristic,random,random --games 200
-python -m wizard_ai serve   # env: SERVER_URL, AI_SHARED_SECRET, AGENT, MODEL_PATH
+python -m wizard_ai serve   # env: SERVER_URL, AI_SHARED_SECRET, AGENT, MODEL_PATH, AI_WORKERS, AI_MAX_QUEUE, AI_DEGRADE_QUEUE
 pytest
 ```