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/sibnet.py

@@ -0,0 +1,85 @@
+from .base import BaseVideoPlayer
+from bs4 import BeautifulSoup
+import re
+from urllib.parse import urljoin
+
+
+class SibnetDownloader(BaseVideoPlayer):
+    """Downloader for sibnet.ru video player"""
+
+    def can_handle(self, url: str) -> bool:
+        return 'sibnet.ru' in url.lower()
+
+    async def get_download_link(self, url: str, target_filename: str = None) -> tuple[str, str]:
+        """
+        Extract download link from Sibnet video page
+        Sibnet uses a JavaScript player with direct MP4 links
+        """
+        try:
+            print(f"[SIBNET] Extracting link from: {url}")
+
+            # If it's already a direct MP4 URL, return it as-is
+            if url.endswith('.mp4'):
+                print(f"[SIBNET] Direct MP4 URL detected")
+                filename = url.split('/')[-1] or "sibnet_video.mp4"
+                return url, filename
+
+            # Fetch the video page
+            response = await self.client.get(
+                url,
+                headers={
+                    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/121.0.0.0 Safari/537.36'
+                }
+            )
+
+            # Parse HTML to find the video source
+            soup = BeautifulSoup(response.text, 'lxml')
+
+            # Look for player.src in JavaScript
+            # Pattern: player.src([{src: "/v/HASH/ID.mp4", type: "video/mp4"},]);
+            script_tags = soup.find_all('script')
+            video_url = None
+
+            for script in script_tags:
+                if script.string:
+                    # Look for player.src pattern
+                    match = re.search(r'player\.src\(\[\{src:\s*"([^"]+\.mp4)"', script.string)
+                    if match:
+                        video_url = match.group(1)
+                        break
+
+                    # Alternative pattern
+                    match = re.search(r'"([^"]+\.mp4)"[^}]*type:\s*"video/mp4"', script.string)
+                    if match:
+                        video_url = match.group(1)
+                        # Make sure it's from /v/ directory
+                        if video_url.startswith('/v/'):
+                            break
+                        video_url = None
+
+            if not video_url:
+                # Try to find any .mp4 URL in the page
+                mp4_match = re.search(r'"/v/[^"]+\.mp4"', response.text)
+                if mp4_match:
+                    video_url = mp4_match.group(0).strip('"')
+
+            if not video_url:
+                raise Exception("Could not find video URL in Sibnet page")
+
+            # Convert relative URL to absolute
+            if video_url.startswith('/'):
+                video_url = urljoin('https://video.sibnet.ru/', video_url)
+
+            print(f"[SIBNET] Found video URL: {video_url[:80]}...")
+
+            # Generate filename from URL or use default
+            filename_match = re.search(r'/([^/]+)\.mp4', video_url)
+            if filename_match:
+                filename = f"{filename_match.group(1)}.mp4"
+            else:
+                filename = "sibnet_video.mp4"
+
+            return video_url, filename
+
+        except Exception as e:
+            raise Exception(f"Error extracting Sibnet link: {str(e)}")