docs: document background jobs across prompts, config example, and README

- Extend the injected Background Jobs prompt guidance: system_notifications
  push on completion, collect-only-when-idle wait protocol, and the graph
  LLM-node collect-before-final-turn rule
- Mention the system_notifications push in the agent spawning guidance and
  in the sisyphus/architect wait-protocol text (agent completions push
  notifications too)
- config.example.yaml: max_concurrent_jobs (default 5, 0 = disabled)
- README: features-list entry pointing at the Background-Jobs wiki page

config.example.yaml

@@ -204,6 +204,7 @@ summary_context_prompt: >        # The text prompt used for including the summar
   'This is a summary of the chat history as a recap: '
 compression_keep_last: 0         # Number of most-recent messages to keep visible after compression (0 = compress all messages)
 max_tool_result_chars: null      # Cap on tool result characters forwarded to the model per call (null = no cap)
+max_concurrent_jobs: 5           # Max background jobs (`job__*` tools) running at once per context (default: 5; 0 disables background jobs entirely)
 
 # ---- Memory ----
 # See the [Memory documentation](https://github.com/Dark-Alex-17/coyote/wiki/Memory) for more information.