docs: describe the document model for tool results

AGENTS.md, README, and /status now describe the request-prep cap and the
document tools (`read_document` / `search_document`). /status also shows the
storage ceiling.

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

tests/test_config/test_agent_section.py

@@ -23,6 +23,7 @@ def test_agent_section_defaults(tmp_path: Path) -> None:
     assert "professional coding agent" in store.agent_config.system_prompt
     assert "### Workspace" in store.agent_config.tool_directives
     assert store.agent_config.max_tool_result_chars == 32_000
+    assert store.agent_config.hard_max_tool_result_chars == 2_000_000
     assert store.agent_config.parallel_tools is True
     assert store.agent_config.confirm_destructive is True
     assert store.agent_config.path_denylist == []