feat: Add SendVid downloader support

Add complete support for SendVid video hosting service used by Anime-Sama
for anime series like Hell's Paradise.

Changes:
- Create SendVidDownloader class with proper headers to avoid 403 errors
- Add SendVid detection and handling in AnimeSamaDownloader
- Update download_manager to include SendVid-specific headers
- Support custom episode naming (e.g., "Hells Paradise - Episode 01.mp4")

Technical details:
- SendVid embed pages require User-Agent and Referer headers
- Direct MP4 URLs extracted from <source> tags with IP/time-based parameters
- Tested with Hell's Paradise Episode 01 (7MB, 24min, 1280x720)

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

app/models/__init__.py

@@ -0,0 +1,42 @@
+from pydantic import BaseModel
+from enum import Enum
+from typing import Optional
+from datetime import datetime
+
+
+class DownloadStatus(str, Enum):
+    PENDING = "pending"
+    DOWNLOADING = "downloading"
+    PAUSED = "paused"
+    COMPLETED = "completed"
+    FAILED = "failed"
+    CANCELLED = "cancelled"
+
+
+class HostType(str, Enum):
+    RAPIDFILE = "rapidfile"
+    UNFICHIER = "1fichier"
+    DOODSTREAM = "doodstream"
+    OTHER = "other"
+
+
+class DownloadTask(BaseModel):
+    id: str
+    url: str
+    filename: str
+    host: HostType
+    status: DownloadStatus
+    progress: float = 0.0
+    downloaded_bytes: int = 0
+    total_bytes: Optional[int] = None
+    speed: float = 0.0
+    error: Optional[str] = None
+    created_at: datetime
+    started_at: Optional[datetime] = None
+    completed_at: Optional[datetime] = None
+    file_path: Optional[str] = None
+
+
+class DownloadRequest(BaseModel):
+    url: str
+    filename: Optional[str] = None