switch nginx-vod-module to the maintained dio-az fork (#24123)

The `v1.x` line is the same muxed fMP4 code as Kaltura's 1.31 with fixes backported, so the mapping JSON, manifest routes, and ffmpeg consumers are unchanged. The `MAX_CLIPS` patch applies as-is and the HEVC workaround is rewritten for the fork's reformatted source.

`vod_hls_version 6` is now explicit because the fork replaced Kaltura's automatic version calculation with a directive that defaults to 4 and only warns when fmp4 needs 6, so playlists were being stamped `EXT-X-VERSION:4` while carrying `EXT-X-MAP`. The `error_page 502 =404` hack is gone: https://github.com/kaltura/nginx-vod-module/issues/468 is a `vod_mode remote` bug and we're `mapped`, so those 502s were really `_vod_response` returning 404 upstream. The fork maps that through now, and the hack was also turning real 5xx into "no recordings".

web/src/components/player/GenericVideoPlayer.tsx

@@ -32,8 +32,8 @@ export function GenericVideoPlayer({
     const checkSourceExists = async (url: string) => {
       try {
         const response = await fetch(url, { method: "HEAD" });
-        // nginx vod module returns 502 for non existent media
-        // https://github.com/kaltura/nginx-vod-module/issues/468
+        // missing media is a 404; 502 still covers a failed or
+        // unreachable mapping request, which is equally unplayable
         setSourceExists(response.status !== 502 && response.status !== 404);
       } catch (error) {
         setSourceExists(false);