refactor: 重构异步任务系统和计费服务架构

- 重构任务系统：新增 lifecycle (TaskStatus/BillingStatus)、context、application 模块
- 将 video tasks 泛化为 async tasks，支持更通用的异步任务管理
- 新增 Gemini Files 管理模块和管理界面
- 重构 billing 服务：拆分 schema.py 和 service.py
- 新增 candidate 服务模块用于请求候选管理
- 数据库迁移：添加 billing_status、request_id、gemini_file_mappings 表和索引
- 移除废弃的 video_telemetry、task orchestrator 等模块

tests/core/api_format/conversion/test_video_format_conversion.py

@@ -0,0 +1,198 @@
+"""
+视频格式转换单元测试
+
+覆盖重点：
+- OpenAI <-> Gemini 视频请求格式转换
+- 视频任务响应格式转换
+"""
+
+from __future__ import annotations
+
+from src.core.api_format.conversion.normalizers.gemini import GeminiNormalizer
+from src.core.api_format.conversion.normalizers.openai import OpenAINormalizer
+from src.core.api_format.conversion.registry import FormatConversionRegistry
+
+
+def _make_registry() -> FormatConversionRegistry:
+    reg = FormatConversionRegistry()
+    reg.register(OpenAINormalizer())
+    reg.register(GeminiNormalizer())
+    return reg
+
+
+class TestVideoRequestConversion:
+    """视频请求格式转换测试"""
+
+    def test_openai_to_gemini_video_request(self) -> None:
+        """OpenAI Sora -> Gemini Veo 请求格式转换"""
+        reg = _make_registry()
+
+        openai_request = {
+            "model": "sora-2",
+            "prompt": "A cat playing piano",
+            "size": "1280x720",
+            "seconds": 8,
+        }
+
+        gemini_request = reg.convert_video_request(openai_request, "openai:video", "gemini:video")
+
+        # 验证 Gemini 格式
+        assert "instances" in gemini_request
+        assert "parameters" in gemini_request
+        assert isinstance(gemini_request["instances"], list)
+        assert len(gemini_request["instances"]) > 0
+
+        instance = gemini_request["instances"][0]
+        assert instance["prompt"] == "A cat playing piano"
+
+        params = gemini_request["parameters"]
+        assert params["aspectRatio"] == "16:9"
+        assert params["resolution"] == "720p"
+        assert params["durationSeconds"] == 8
+
+    def test_gemini_to_openai_video_request(self) -> None:
+        """Gemini Veo -> OpenAI Sora 请求格式转换"""
+        reg = _make_registry()
+
+        gemini_request = {
+            "model": "veo-3.1-generate-preview",
+            "instances": [{"prompt": "A beautiful sunset over mountains"}],
+            "parameters": {
+                "aspectRatio": "16:9",
+                "resolution": "1080p",
+                "durationSeconds": 5,
+            },
+        }
+
+        openai_request = reg.convert_video_request(gemini_request, "gemini:video", "openai:video")
+
+        # 验证 OpenAI 格式
+        assert openai_request["prompt"] == "A beautiful sunset over mountains"
+        assert openai_request["model"] == "veo-3.1-generate-preview"
+        assert openai_request["seconds"] == 5
+        assert openai_request["size"] == "1920x1080"
+
+    def test_same_format_no_conversion(self) -> None:
+        """相同格式不进行转换"""
+        reg = _make_registry()
+
+        openai_request = {
+            "model": "sora-2",
+            "prompt": "Test",
+            "size": "720x1280",
+            "seconds": 4,
+        }
+
+        result = reg.convert_video_request(openai_request, "openai:video", "openai:video")
+        assert result == openai_request
+
+    def test_conversion_with_reference_image(self) -> None:
+        """带参考图片的请求转换"""
+        reg = _make_registry()
+
+        openai_request = {
+            "model": "sora-2",
+            "prompt": "Animate this image",
+            "size": "1280x720",
+            "seconds": 4,
+            "input_reference": "base64_encoded_image_data",
+        }
+
+        gemini_request = reg.convert_video_request(openai_request, "openai:video", "gemini:video")
+
+        instance = gemini_request["instances"][0]
+        assert "image" in instance
+        assert instance["image"]["bytesBase64Encoded"] == "base64_encoded_image_data"
+
+
+class TestVideoTaskConversion:
+    """视频任务响应格式转换测试"""
+
+    def test_gemini_to_openai_processing_task(self) -> None:
+        """Gemini 处理中任务 -> OpenAI 格式"""
+        reg = _make_registry()
+
+        gemini_response = {
+            "name": "operations/12345",
+            "done": False,
+            "metadata": {"progress": 50},
+        }
+
+        openai_response = reg.convert_video_task(gemini_response, "gemini:video", "openai:video")
+
+        # OpenAI 格式使用 status 字段
+        assert openai_response["status"] in ("queued", "processing")
+        assert "id" in openai_response
+
+    def test_gemini_to_openai_completed_task(self) -> None:
+        """Gemini 完成任务 -> OpenAI 格式"""
+        reg = _make_registry()
+
+        gemini_response = {
+            "name": "operations/12345",
+            "done": True,
+            "response": {
+                "generateVideoResponse": {
+                    "generatedSamples": [{"video": {"uri": "https://example.com/video.mp4"}}]
+                }
+            },
+        }
+
+        openai_response = reg.convert_video_task(gemini_response, "gemini:video", "openai:video")
+
+        assert openai_response["status"] == "completed"
+        assert openai_response["progress"] == 100
+
+    def test_openai_to_gemini_processing_task(self) -> None:
+        """OpenAI 处理中任务 -> Gemini 格式"""
+        reg = _make_registry()
+
+        openai_response = {
+            "id": "task_12345",
+            "object": "video",
+            "status": "processing",
+            "progress": 30,
+            "created_at": 1700000000,
+        }
+
+        gemini_response = reg.convert_video_task(openai_response, "openai:video", "gemini:video")
+
+        # Gemini 格式使用 done 字段
+        assert gemini_response["done"] is False
+        assert "name" in gemini_response
+
+    def test_openai_to_gemini_completed_task(self) -> None:
+        """OpenAI 完成任务 -> Gemini 格式"""
+        reg = _make_registry()
+
+        openai_response = {
+            "id": "task_12345",
+            "object": "video",
+            "status": "completed",
+            "progress": 100,
+            "created_at": 1700000000,
+            "completed_at": 1700000100,
+        }
+
+        gemini_response = reg.convert_video_task(openai_response, "openai:video", "gemini:video")
+
+        assert gemini_response["done"] is True
+
+
+class TestVideoConversionCapabilities:
+    """视频格式转换能力检查测试"""
+
+    def test_can_convert_video(self) -> None:
+        """检查视频格式转换能力"""
+        reg = _make_registry()
+
+        assert reg.can_convert_video("openai:video", "gemini:video") is True
+        assert reg.can_convert_video("gemini:video", "openai:video") is True
+        assert reg.can_convert_video("openai:video", "openai:video") is True
+
+    def test_cannot_convert_unsupported_format(self) -> None:
+        """不支持的格式无法转换"""
+        reg = _make_registry()
+
+        # 没有注册 Claude normalizer 用于视频
+        assert reg.can_convert_video("openai:video", "claude:video") is False