fix springfiles probe: lowercase filename in URL

Springfiles is Apache on Linux (case-sensitive) and stores all 3570 of
its map filenames lowercase — verified against the live catalog, zero
exceptions. ZK keeps original casing on ResourceContentFile.FileName
(e.g. Sever_1.sd7, Gasbag_Grabens_1.1.1.sd7), so the HEAD probe at
.../files/maps/{cf.FileName} returns 404 for every CamelCase map, the
probe writes LinkCount=0, and the result sticks for 24 h.

Affects far more than the 5 maps in #3057 — any map whose original
upload preserved capital letters has had a permanently-broken SF mirror.

Lowercased the filename component in the three places that build the
springfiles URL (BuildLinks, RunProbe's inner cache check, ProbeAndAssign).
The local URL keeps original casing — IIS on the ZK host is
case-insensitive, no change needed there.

Existing cached state with the old mixed-case URL stays "missing" until
the natural 24 h cache expiry, at which point each map gets re-probed
with the lowercased URL and recovers.

Author: Licho1

Zero-K.info/AppCode/ResourceLinkProvider.cs

@@ -72,7 +72,9 @@ public static List<string> BuildLinks(ResourceContentFile content)
 
             var subfolder = content.Resource.TypeID == ResourceType.Map ? "maps" : "games";
             var localUrl = $"{GlobalConst.BaseSiteUrl}/content/{subfolder}/{content.FileName}";
-            var springfilesUrl = $"{GlobalConst.SpringfilesBaseUrl}files/{subfolder}/{content.FileName}";
+            // springfiles runs on case-sensitive Apache and stores all 3500+ map filenames lowercase;
+            // probing with mixed-case yields 404 even when the map is there.
+            var springfilesUrl = $"{GlobalConst.SpringfilesBaseUrl}files/{subfolder}/{content.FileName.ToLower()}";
 
             var links = new List<string>();
             if (File.Exists(Global.MapPath($"~/content/{subfolder}/{content.FileName}"))) links.Add(localUrl);
@@ -132,7 +134,7 @@ static bool RunProbe(string md5)
                         && DateTime.UtcNow.Subtract(cf.Resource.LastLinkCheck.Value).TotalHours < SpringfilesRecheckHours)
                     {
                         var subfolder = cf.Resource.TypeID == ResourceType.Map ? "maps" : "games";
-                        var springfilesUrl = $"{GlobalConst.SpringfilesBaseUrl}files/{subfolder}/{cf.FileName}";
+                        var springfilesUrl = $"{GlobalConst.SpringfilesBaseUrl}files/{subfolder}/{cf.FileName.ToLower()}";
                         return !string.IsNullOrEmpty(cf.Links) && cf.Links.Split('\n').Contains(springfilesUrl);
                     }
 
@@ -169,7 +171,8 @@ static bool ProbeAndAssign(ResourceContentFile cf)
         {
             var subfolder = cf.Resource.TypeID == ResourceType.Map ? "maps" : "games";
             var localUrl = $"{GlobalConst.BaseSiteUrl}/content/{subfolder}/{cf.FileName}";
-            var springfilesUrl = $"{GlobalConst.SpringfilesBaseUrl}files/{subfolder}/{cf.FileName}";
+            // SF stores all map filenames lowercase; see BuildLinks for the rationale.
+            var springfilesUrl = $"{GlobalConst.SpringfilesBaseUrl}files/{subfolder}/{cf.FileName.ToLower()}";
 
             var hasSpringfiles = HeadCheck(springfilesUrl, cf.Length);