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/app/call_log.py

@@ -16,12 +16,21 @@ from . import config
 
 
 def _default_write(line: str) -> None:
-    path = config.call_log_path()
-    if path:
-        with open(path, "a", encoding="utf-8") as handle:
-            handle.write(line + "\n")
-    else:
-        sys.stdout.write(line + "\n")
+    """Best-effort (charter §13): a good model call must never become a 500
+    because the log write failed (disk full, bad permissions, a misconfigured
+    CALL_LOG_PATH). Any failure here is swallowed and reported to stderr —
+    never stdout, since stdout may itself be the default sink and must stay
+    clean JSON-lines for downstream tooling.
+    """
+    try:
+        path = config.call_log_path()
+        if path:
+            with open(path, "a", encoding="utf-8") as handle:
+                handle.write(line + "\n")
+        else:
+            sys.stdout.write(line + "\n")
+    except Exception as exc:  # noqa: BLE001 - logging must never break a request
+        print(f"call_log: failed to write log line: {exc}", file=sys.stderr)
 
 
 def record(