refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/tests/test_interview_turn_plan.py

@@ -296,3 +296,11 @@ def test_build_topic_chips_english_uses_slot_name_map_en():
     place_chip = next(c for c in chips if c["id"] == "place")
     assert place_chip["label"] == "where you grew up"
     assert place_chip["text"].startswith("I'd like to talk about")
+
+
+def test_build_topic_chips_belief_stage_not_empty():
+    from app.agents.chat.prompts_conversation import build_topic_chips
+
+    chips = build_topic_chips("belief", [], max_chips=4, language="en")
+    assert len(chips) == 4
+    assert chips[0]["label"]