fix(api): best-effort call logging + non-JSON 200 → ModelError (final-review)

- call_log._default_write: swallow any exception from the default file/
  stdout sink and report to stderr, so a log-write failure (disk full,
  bad permissions, misconfigured CALL_LOG_PATH) never turns a successful
  narration into a 500 (charter §13). Injected write= sinks (used by
  tests) are left to surface their own errors.
- ollama_client.chat: catch ValueError alongside httpx.HTTPError in the
  retry loop so a 200 response with a non-JSON body (JSONDecodeError is
  a ValueError subclass) counts as a failed attempt and falls through to
  ModelError after the one retry, instead of escaping chat() uncaught
  (charter §12 — one retry, then ModelError, nothing else escapes).
- main.py: update stale docstrings — /dm/narrate is now fully wired
  (routing + model call + logging); the other four roles remain stubs.

Regression tests added for both fixes (TDD: watched RED, then GREEN).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/tests/test_call_log.py

@@ -32,3 +32,25 @@ def test_failure_record_shape():
     assert parsed["ok"] is False
     assert parsed["error"] == "ModelError: down"
     assert "response" not in parsed
+
+
+def test_default_write_failure_does_not_propagate(monkeypatch, capsys):
+    """§13 — a good narration must never become a 500 because the log write
+    failed. Point CALL_LOG_PATH at a path whose parent directory does not
+    exist, so the default sink's `open()` raises. record() must swallow it,
+    report to stderr (never stdout — stdout may be the log sink itself), and
+    still return the record.
+    """
+    monkeypatch.setenv(
+        "CALL_LOG_PATH", "/nonexistent-dir-for-test/does/not/exist.log"
+    )
+    rec = record(
+        role="narrator", model="qwen3.5:latest", options={"seed": 7},
+        messages=[{"role": "user", "content": "x"}], canon_log={"a": 1},
+        ok=True, latency_ms=120, response="prose",
+    )
+    assert rec["response"] == "prose"
+    assert rec["ok"] is True
+    out, err = capsys.readouterr()
+    assert out == ""
+    assert err != ""