feat: wire videy + tiktok/v2 + twitter/v2 downloader endpoints

Ported all missing downloader endpoints from Shirokami-API source
(verified against /home/code/Shirokami-API/scraper/downloader/):

- /download/videy: direct CDN link build (cdn.videy.co/{id}.mp4|.mov)
  matches videy.js exactly (id.len()==9 && id[8]=='2' -> .mov)
- /download/tiktok/v2: douyin.wtf hybrid API w/ fallback to embed scrape
- /download/twitter/v2: twitsave.com HTML scrape w/ fallback to Syndication API
- detect_platform now recognizes videy.co
- download_all_in_one dispatches videy

fetch_videy already existed as dead code (never wired); connected it.
== all others (bilibili/danbooru/dood/gdrive/instagram/kfiles/mediafire/
== mega/pinterest/pixeldrain/savetube/soundcloud/spotify/terabox/threads/
== tiktok/twitter/youtubeV2) already mapped to their Rust equivalents

src/application/downloader.rs

@@ -119,6 +119,18 @@ pub async fn download_streamable(url: &str) -> Result<DownloadResult, ScrapingEr
     DownloaderRepository::download_streamable(url).await
 }
 
+pub async fn download_videy(url: &str) -> Result<DownloadResult, ScrapingError> {
+    DownloaderRepository::download_videy(url).await
+}
+
+pub async fn download_tiktok_v2(url: &str) -> Result<DownloadResult, ScrapingError> {
+    DownloaderRepository::download_tiktok_v2(url, None).await
+}
+
+pub async fn download_twitter_v2(url: &str) -> Result<DownloadResult, ScrapingError> {
+    DownloaderRepository::download_twitter_v2(url, None).await
+}
+
 pub async fn download_bilibili(url: &str) -> Result<DownloadResult, ScrapingError> {
     DownloaderRepository::download_bilibili(url).await
 }
@@ -165,6 +177,8 @@ pub fn detect_platform(url: &str) -> String {
         "dailymotion".to_string()
     } else if url.contains("streamable.com") {
         "streamable".to_string()
+    } else if url.contains("videy.co") {
+        "videy".to_string()
     } else if url.contains("bilibili.com") || url.contains("b23.tv") {
         "bilibili".to_string()
     } else {