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_default_toml_legacy_parity.py

@@ -0,0 +1,23 @@
+"""Guard: config/default.toml defaults stay aligned with pre-TOML Settings."""
+
+from app.core.app_config_loader import default_config_dir, load_app_config
+
+
+def test_default_toml_matches_legacy_settings_defaults() -> None:
+    cfg = load_app_config("development", config_dir=default_config_dir())
+
+    assert cfg.chat.interview_persona == "default"
+    assert cfg.chat.interview_temperature == 0.93
+    assert cfg.chat.memory_top_k == 8
+    assert cfg.chat.memory_evidence_max_chars == 4096
+    assert cfg.chat.reply_planner_llm_enabled is False
+
+    assert cfg.memoir.oral_normalize_mode == "rules"
+
+    assert cfg.story.image_min_body_chars == 400
+
+    assert cfg.asr.provider == "whisper"
+    assert cfg.asr.device == "auto"
+    assert cfg.asr.compute_type == "auto"
+
+    assert cfg.misc.tencent_sms_template_param_count == 2