refactor: Restructure downloaders with clear separation

This commit implements a complete reorganization of the downloader system
with a clear distinction between anime streaming sites and video hosting services.

## Structure Changes

**New Organization:**
- `app/downloaders/anime_sites/` - Anime streaming sites (catalogs + metadata)
- `app/downloaders/video_players/` - Video hosting services (file downloads)

**Base Classes:**
- `BaseAnimeSite` - For anime providers (search, episodes, metadata)
- `BaseVideoPlayer` - For video players (download link extraction)

**Migrated Downloaders:**
Anime Sites (4):
- AnimeSama, NekoSama, AnimeUltime, Vostfree

Video Players (8):
- Doodstream, Sibnet, VidMoly, SendVid, Lpayer, 1fichier, Uptobox, Rapidfile

## Key Improvements

1. **Clear Separation**: Distinct base classes for different use cases
2. **Preserved Functionality**: All existing features maintained
   - VidMoly: M3U8 support, Playwright, multi-domains, target_filename param
   - SendVid: target_filename parameter support
   - All others: No behavioral changes

3. **Better Organization**:
   - Anime sites: search_anime(), get_episodes(), get_anime_metadata()
   - Video players: get_download_link(url, target_filename=None)

4. **Fixed Imports**: Updated cross-imports in AnimeSama
   - from ..video_players.vidmoly import
   - from ..video_players.sendvid import
   - from ..video_players.sibnet import
   - from ..video_players.lpayer import

5. **Updated Tests**: All test imports use new structure
6. **Updated Providers**: Added 4 missing file hosts to providers.py

## Backward Compatibility

✅ Main API unchanged: get_downloader() works identically
✅ All 23 tests passing
✅ Frontend fully functional
✅ No breaking changes for users

## Documentation

- RESTRUCTURATION_SUMMARY.md - Technical details
- FIX_IMPORT_ERROR.md - Import error resolution
- IMPORT_VERIFICATION_REPORT.md - Complete import verification
- FRONTEND_VERIFICATION_FINAL.md - Frontend validation

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/downloaders/video_players/base.py

@@ -0,0 +1,85 @@
+"""Base class for video hosting services (players)"""
+from abc import abstractmethod
+from typing import Optional, Tuple
+import logging
+import httpx
+from bs4 import BeautifulSoup
+
+logger = logging.getLogger(__name__)
+
+
+class BaseVideoPlayer:
+    """
+    Base class for video hosting services.
+
+    Video players host actual video files and provide direct download links.
+    They extract URLs from embedded players and handle file downloads.
+
+    Examples: Doodstream, Sibnet, VidMoly, SendVid, Lpayer, 1fichier, etc.
+
+    KEY FEATURE: Flexible get_download_link() signature to support:
+    - Standard: get_download_link(url)
+    - With target_filename: get_download_link(url, target_filename="...")  (VidMoly, SendVid)
+    """
+
+    def __init__(self):
+        # Initialize HTTP client directly
+        self.client = httpx.AsyncClient(timeout=10.0, follow_redirects=True)
+
+    @abstractmethod
+    def can_handle(self, url: str) -> bool:
+        """Check if this player can handle the given URL"""
+        pass
+
+    @abstractmethod
+    async def get_download_link(
+        self,
+        url: str,
+        target_filename: Optional[str] = None
+    ) -> Tuple[str, str]:
+        """
+        Extract direct download link and filename from video player URL.
+
+        Args:
+            url: The video player URL
+            target_filename: Optional filename override (used by VidMoly, SendVid)
+
+        Returns:
+            Tuple of (download_url, filename)
+
+        Note:
+            - Always use sanitize_filename() on extracted filenames!
+            - target_filename parameter is optional but MUST be supported
+              for compatibility with VidMoly and SendVid
+        """
+        pass
+
+    # Common methods for all video players
+    async def close(self):
+        """Close HTTP client"""
+        await self.client.aclose()
+
+    async def _fetch_page(self, url: str) -> str:
+        """Fetch HTML page content"""
+        response = await self.client.get(url)
+        response.raise_for_status()
+        return response.text
+
+    def _parse_html(self, html: str) -> BeautifulSoup:
+        """Parse HTML with BeautifulSoup"""
+        return BeautifulSoup(html, 'lxml')
+
+    def _extract_filename_from_headers(self, headers: dict) -> Optional[str]:
+        """Extract filename from Content-Disposition header"""
+        from app.utils import sanitize_filename
+
+        content_disposition = headers.get("content-disposition", "")
+        if "filename=" in content_disposition:
+            filename = content_disposition.split("filename=")[-1].strip('"')
+            return sanitize_filename(filename)  # Security!
+        return None
+
+    def _sanitize(self, filename: str) -> str:
+        """Convenience method for filename sanitization"""
+        from app.utils import sanitize_filename
+        return sanitize_filename(filename)