Phase 2b: server/client timeouts, atomic state writes, log mutex, panic and shutdown fixes

- http.Server with ReadHeaderTimeout/IdleTimeout (no read/write timeouts: /stream/ is long-lived)
- shared outbound clients: providerHTTPClient (5m), apiHTTPClient (30s), imgcache client (30s)
- imgcache: download outside the lock, per-item helper, cache URL uses the file name not the fs path
- writeFileAtomic (temp + fsync + rename) for settings/xepg/pms/urls/authentication JSON
- one package-level logMu for WebScreenLog and notifications; ring buffer keeps the newest lines
- notifications evict the oldest instead of random map entries
- xepg XMLTV file removal rebuilt after the loop; data.go range-mutation removed
- API handler returns after error body; WS request/response fresh per command
- checked type assertions in data/backup/provider/screen
- SIGINT/SIGTERM handled in main via src.Shutdown(); fatal paths exit 1

src/xepg.go

@@ -172,6 +172,11 @@ func createXEPGMapping() {
 
 	if len(Data.XMLTV.Files) > 0 {
 
+		// Files that could not be read are collected here and removed after
+		// the loop; mutating Data.XMLTV.Files while iterating over it used
+		// to duplicate entries instead of removing them.
+		var failedFiles = make(map[string]bool)
+
 		for i := len(Data.XMLTV.Files) - 1; i >= 0; i-- {
 
 			var file = Data.XMLTV.Files[i]
@@ -185,7 +190,7 @@ func createXEPGMapping() {
 
 			err = getLocalXMLTV(file, &xmltv)
 			if err != nil {
-				Data.XMLTV.Files = append(Data.XMLTV.Files, Data.XMLTV.Files[i+1:]...)
+				failedFiles[file] = true
 				var errMsg = err.Error()
 				err = errors.New(getProviderParameter(fileID, "xmltv", "name") + ": " + errMsg)
 				ShowError(err, 000)
@@ -215,6 +220,7 @@ func createXEPGMapping() {
 
 		}
 
+		Data.XMLTV.Files = removeStrings(Data.XMLTV.Files, failedFiles)
 		Data.XMLTV.Mapping = tmpMap
 
 	} else {