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/app/features/auth/integrity.py

@@ -0,0 +1,42 @@
+"""Map users-table unique constraint violations to auth error codes."""
+
+from __future__ import annotations
+
+from sqlalchemy.exc import IntegrityError
+
+_PHONE_CONSTRAINT_MARKERS = frozenset({"phone", "ix_users_phone", "users_phone_key"})
+_EMAIL_CONSTRAINT_MARKERS = frozenset({"email", "users_email_key", "ix_users_email"})
+
+
+def _constraint_text(exc: IntegrityError) -> str:
+    orig = exc.orig
+    if orig is None:
+        return str(exc).lower()
+    diag = getattr(orig, "diag", None)
+    if diag is not None:
+        name = getattr(diag, "constraint_name", None)
+        if name:
+            return str(name).lower()
+    return str(orig).lower()
+
+
+def _matches(markers: frozenset[str], text: str) -> bool:
+    return any(marker in text for marker in markers)
+
+
+def user_integrity_auth_code(
+    exc: IntegrityError,
+    *,
+    phone_conflict: str,
+) -> str | None:
+    """Return auth internal code for a users-table unique violation, or None."""
+    text = _constraint_text(exc)
+    if _matches(_PHONE_CONSTRAINT_MARKERS, text):
+        return phone_conflict
+    if _matches(_EMAIL_CONSTRAINT_MARKERS, text):
+        return "EMAIL_EXISTS"
+    return None
+
+
+def is_user_phone_unique_violation(exc: IntegrityError) -> bool:
+    return _matches(_PHONE_CONSTRAINT_MARKERS, _constraint_text(exc))