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

xteve.go

@@ -9,9 +9,11 @@ import (
 	"flag"
 	"fmt"
 	"os"
+	"os/signal"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"syscall"
 
 	"xteve/src"
 )
@@ -111,7 +113,7 @@ func main() {
 		err := src.Init()
 		if err != nil {
 			src.ShowError(err, 0)
-			os.Exit(0)
+			os.Exit(1)
 		}
 
 		src.ShowSystemInfo()
@@ -150,12 +152,13 @@ func main() {
 		err := src.Init()
 		if err != nil {
 			src.ShowError(err, 0)
-			os.Exit(0)
+			os.Exit(1)
 		}
 
 		err = src.XteveRestoreFromCLI(*restore)
 		if err != nil {
 			src.ShowError(err, 0)
+			os.Exit(1)
 		}
 
 		os.Exit(0)
@@ -164,25 +167,35 @@ func main() {
 	err := src.Init()
 	if err != nil {
 		src.ShowError(err, 0)
-		os.Exit(0)
+		os.Exit(1)
 	}
 
 	err = src.StartSystem(false)
 	if err != nil {
 		src.ShowError(err, 0)
-		os.Exit(0)
+		os.Exit(1)
 	}
 
+	// Graceful stop on SIGINT / SIGTERM: say goodbye on the network (SSDP)
+	// and exit cleanly instead of letting the runtime kill the process.
+	go func() {
+		quit := make(chan os.Signal, 1)
+		signal.Notify(quit, os.Interrupt, syscall.SIGTERM)
+		<-quit
+		src.Shutdown()
+		os.Exit(0)
+	}()
+
 	err = src.InitMaintenance()
 	if err != nil {
 		src.ShowError(err, 0)
-		os.Exit(0)
+		os.Exit(1)
 	}
 
 	err = src.StartWebserver()
 	if err != nil {
 		src.ShowError(err, 0)
-		os.Exit(0)
+		os.Exit(1)
 	}
 
 }