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/downloaders/rapidfile.py

@@ -0,0 +1,75 @@
+from .base import BaseDownloader
+from bs4 import BeautifulSoup
+import re
+import httpx
+
+
+class RapidFileDownloader(BaseDownloader):
+    """Downloader for rapidfile.net and similar hosts"""
+
+    def can_handle(self, url: str) -> bool:
+        return any(domain in url.lower() for domain in ["rapidfile.net", "rapidfile.com", "rapid-file"])
+
+    async def get_download_link(self, url: str) -> tuple[str, str]:
+        try:
+            # Get the initial page
+            response = await self.client.get(url)
+            response.raise_for_status()
+            soup = BeautifulSoup(response.text, 'lxml')
+
+            download_url = None
+            filename = "rapidfile_download"
+
+            # Method 1: Look for download button/link
+            download_btn = soup.find('a', {'id': 'downloadbtn'}) or soup.find('a', class_='download-btn')
+            if download_btn and download_btn.get('href'):
+                download_url = download_btn['href']
+
+            # Method 2: Look for form with POST action
+            if not download_url:
+                forms = soup.find_all('form')
+                for form in forms:
+                    action = form.get('action', '')
+                    if action and ('download' in action.lower() or 'file' in action.lower()):
+                        download_url = action if action.startswith('http') else url + action
+                        break
+
+            # Method 3: Look for any link with download/file in URL
+            if not download_url:
+                for link in soup.find_all('a', href=True):
+                    href = link['href']
+                    if any(keyword in href.lower() for keyword in ['download', 'get_file', 'file.php']):
+                        if href.startswith('http'):
+                            download_url = href
+                            break
+
+            # Method 4: Check for direct file links in scripts
+            if not download_url:
+                scripts = soup.find_all('script')
+                for script in scripts:
+                    if script.string:
+                        match = re.search(r'(https?://[^\s\"\'<>]+/(?:download|file)[^\s\"\'<>]+)', script.string)
+                        if match:
+                            download_url = match.group(0)
+                            break
+
+            if download_url:
+                # Get filename from headers or URL
+                try:
+                    head_resp = await self.client.head(download_url, timeout=5.0)
+                    fname = self._extract_filename_from_headers(head_resp.headers)
+                    if fname:
+                        filename = fname
+                    else:
+                        filename = download_url.split('/')[-1] or "rapidfile_download"
+                except:
+                    filename = download_url.split('/')[-1] or "rapidfile_download"
+
+                return download_url, filename
+
+            # If all else fails, return the original URL
+            filename = url.split('/')[-1] or "rapidfile_download"
+            return url, filename
+
+        except Exception as e:
+            raise Exception(f"Error extracting Rapidfile link: {str(e)}")