Make the config file the only home for settings

With no production instance yet, there is no reason to carry two ways
of configuring the agent. Every environment variable that duplicated a
config key is gone; the environment now supplies only the secrets the
file references by ${…}, plus NISSE_CONFIG and NISSE_ENV to find the
files.

- AgentConfig loads from a file (load, from_file) or a parsed tree
  (from_tree, for tests); a missing file is an error naming the example
- The from_env constructors on LiteLLMClient, AnthropicPassthroughClient,
  GiteaClient, MatrixConfig and RoleMap are removed, with the env
  reading for max output tokens; clients take their settings from config
- The live integration tests share a committed agent config,
  tests/integration/nisse-test.yaml, aimed at test resources, and one
  conftest that loads it and builds clients. NISSE_LIVE_PLANNER_MODEL
  becomes its planner role; NISSE_CAPABILITY_MODELS stays as a per-run
  switch
- A missing secret now fails the live tests instead of skipping them
- CI passes only the three tokens
- .env.example is secrets only; spec A5 says config comes from the file

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/integration/test_llm_live.py

@@ -1,41 +1,17 @@
-"""Live smoke test against the real LiteLLM proxy.
-
-NISSE_LLM_BASE_URL alone decides whether this runs: if it is set, the live
-path is expected to work, and anything else missing is a *failure*, not a
-skip. A half-configured environment must not pass quietly as a skip — that is
-how a broken CI credential hides.
-"""
-
-import os
-from pathlib import Path
+"""Live smoke test against the real LiteLLM proxy."""
 
 import pytest
 
 from nisse_dev.canonical import AssistantText, StoredEvent, UserMessage
-from nisse_dev.envfile import load_env_file
+from nisse_dev.config import AgentConfig
 from nisse_dev.llm import LiteLLMClient
 
-load_env_file(Path(__file__).resolve().parents[2] / ".env")
-
-SENTINEL = "NISSE_LLM_BASE_URL"
-ALSO_REQUIRED = ("NISSE_LLM_TOKEN", "NISSE_ROLE_EXECUTOR")
-
-pytestmark = [
-    pytest.mark.integration,
-    pytest.mark.skipif(
-        not os.environ.get(SENTINEL),
-        reason=f"no live LLM configured ({SENTINEL} unset)",
-    ),
-]
+pytestmark = pytest.mark.integration
 
 
-def test_executor_model_completes_via_litellm() -> None:
-    missing = [var for var in ALSO_REQUIRED if not os.environ.get(var)]
-    assert not missing, (
-        f"{SENTINEL} is set, so the live LLM path is expected to work, "
-        f"but these are missing: {', '.join(missing)}"
-    )
-    client = LiteLLMClient.from_env()
+def test_executor_model_completes_via_litellm(
+    litellm: LiteLLMClient, live_config: AgentConfig
+) -> None:
     events = [
         StoredEvent(
             id=1,
@@ -45,9 +21,7 @@ def test_executor_model_completes_via_litellm() -> None:
             ),
         )
     ]
-    result = client.complete(
-        events, tools=None, model=os.environ["NISSE_ROLE_EXECUTOR"]
-    )
+    result = litellm.complete(events, tools=None, model=live_config.roles.executor)
     texts = [e.text for e in result if isinstance(e, AssistantText)]
     assert texts, f"no assistant text in {result!r}"
     assert "pong" in texts[0].lower()