feat(backend): Phase 1 数据层 — Domain / Provider / Failover 审计 + 持久化 + 同步 CLI

- domain：市场数据实体（Stock / 交易日历 / 日线 / 复权 / 财务含 announce_date）+ Repository 与 MarketDataProvider Protocol
- 数据源：TushareProvider（归一化、重试、鉴权错误归类）、SinaProvider（备用，明确前复权口径与能力边界）、FailoverProvider + SyncLog 审计（禁止静默切换）
- 持久化：SQLAlchemy 2.x Models + Repository 实现（按业务键幂等 upsert、as_of_date 防未来函数过滤）+ Alembic 迁移
- CLI：uv run python -m app.cli.sync {basic|calendar|daily|financial|verify}，支持 --resume 断点续传
- 真实 Tushare 验证：stock 5556 / 交易日历 366 / daily+factor 242 / 财务 55；sync_log 审计完整
- 测试：38 passed（domain / provider / failover / repository / 未来函数 / 迁移），ruff clean

backend/tests/test_failover.py

@@ -0,0 +1,93 @@
+"""Failover 审计测试：主源失败 → 备用源兜底，每次尝试留 SyncLog。"""
+
+from __future__ import annotations
+
+from datetime import date
+
+import pytest
+from app.domain.entities.market import SyncLog
+from app.infrastructure.data_sources.errors import (
+    DataSourceError,
+    DataSourceNotSupported,
+)
+from app.infrastructure.data_sources.failover import FailoverProvider
+
+
+class PrimaryProvider:
+    name = "tushare"
+
+    def __init__(self, *, fail: bool = False, fail_message: str = "boom") -> None:
+        self.fail = fail
+        self.fail_message = fail_message
+
+    def get_daily(self, symbol, start, end):
+        if self.fail:
+            raise DataSourceError(self.fail_message)
+        return ["bar-ok"]
+
+
+class FallbackProvider:
+    name = "sina"
+
+    def __init__(self, *, fail: bool = False, unsupported: bool = False) -> None:
+        self.fail = fail
+        self.unsupported = unsupported
+
+    def get_daily(self, symbol, start, end):
+        if self.unsupported:
+            raise DataSourceNotSupported("新浪不支持日线兜底")
+        if self.fail:
+            raise DataSourceError("sina down")
+        return ["bar-sina"]
+
+
+def _logs() -> list[SyncLog]:
+    collected: list[SyncLog] = []
+    return collected
+
+
+def _make(primary, fallback, collected) -> FailoverProvider:
+    return FailoverProvider(primary, fallback, audit=collected.append)
+
+
+class TestFailover:
+    def test_primary_success_no_fallback(self) -> None:
+        collected: list[SyncLog] = []
+        f = _make(PrimaryProvider(), FallbackProvider(), collected)
+        assert f.get_daily("600519.SH", date(2024, 1, 1), date(2024, 1, 5)) == ["bar-ok"]
+        assert len(collected) == 1
+        assert collected[0].source == "tushare"
+        assert collected[0].success is True
+        assert collected[0].row_count == 1
+        assert collected[0].data_start == date(2024, 1, 1)
+
+    def test_primary_fails_fallback_succeeds(self) -> None:
+        collected: list[SyncLog] = []
+        f = _make(PrimaryProvider(fail=True), FallbackProvider(), collected)
+        assert f.get_daily("600519.SH", date(2024, 1, 1), date(2024, 1, 5)) == ["bar-sina"]
+        assert [log.source for log in collected] == ["tushare", "sina"]
+        assert collected[0].success is False
+        assert "boom" in (collected[0].failure_reason or "")
+        assert collected[1].success is True
+
+    def test_fallback_unsupported_raises_with_audit(self) -> None:
+        collected: list[SyncLog] = []
+        f = _make(PrimaryProvider(fail=True), FallbackProvider(unsupported=True), collected)
+        with pytest.raises(DataSourceError, match="备用源不支持"):
+            f.get_daily("600519.SH", date(2024, 1, 1), date(2024, 1, 5))
+        assert len(collected) == 2
+        assert collected[1].success is False
+
+    def test_both_fail_raises_with_audit(self) -> None:
+        collected: list[SyncLog] = []
+        f = _make(PrimaryProvider(fail=True), FallbackProvider(fail=True), collected)
+        with pytest.raises(DataSourceError, match="主备数据源均失败"):
+            f.get_daily("600519.SH", date(2024, 1, 1), date(2024, 1, 5))
+        assert len(collected) == 2
+
+    def test_no_fallback_raises(self) -> None:
+        collected: list[SyncLog] = []
+        f = FailoverProvider(PrimaryProvider(fail=True), None, audit=collected.append)
+        with pytest.raises(DataSourceError, match="无备用源"):
+            f.get_daily("600519.SH", date(2024, 1, 1), date(2024, 1, 5))
+        assert len(collected) == 1