fix(ai): bound response parsing and harden AUTO fallback errors

- bound _parse_responses scans to the output_text part's object and to
  the content array, so a later sibling item's "text" (e.g. a reasoning
  summary) can never be returned as the assistant reply
- do not retry the other flavour on a curl timeout: the request likely
  reached the server and may still be generating, so a re-POST of the
  conversation could trigger a second billed generation
- remember an unparseable 2xx from the first AUTO attempt and surface
  stashed first-attempt errors in both error paths, instead of showing
  only the final attempt's transport or HTTP error
- recognize Ollama's model-not-found wording in _names_model so a model
  typo is not misread as a missing endpoint
- drop the dead, racy provider-lookup fallback in the generic request
  thread: a missing provider ref is a caller bug and now fails loudly
- fix ai_providers_lists_defaults to expect the header the command
  actually prints ("Configured providers:"); the test was broken since
  its introduction but CI never ran it
- add functional test group 5 (AI command surface) to FUNC_TEST_GROUPS
  so the CI parallel target runs it; proftest.c port ranges already
  account for five groups

src/ai/ai_client.c

@@ -2186,7 +2186,7 @@ _ai_request_thread(gpointer data)
                          ai_api_type_to_string(attempts[i + 1]));
                 if (!first_unparsable_note)
                     first_unparsable_note = g_strdup_printf("%s endpoint answered HTTP %ld but the body could not be parsed",
-                                                            ai_api_type_to_string(used_type), http_code);
+                                                             ai_api_type_to_string(used_type), http_code);
                 continue;
             }
         }