feat: add structured logging with log/slog and panic recovery

Replace log.Printf/Println with slog.Info/Error/Warn across the codebase.
Initialize slog with JSON handler in main.go. Add panic recovery defer
in SSH session handler. Add structured game event logging (room created,
player joined, game started, game over, player inactive removed).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"log"
+	"log/slog"
 	"os"
 
 	"github.com/tolelom/catacombs/config"
@@ -15,6 +16,11 @@ import (
 func main() {
 	os.MkdirAll("data", 0755)
 
+	logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	}))
+	slog.SetDefault(logger)
+
 	cfg, err := config.Load("config.yaml")
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -38,11 +44,11 @@ func main() {
 	// Start web terminal server in background
 	go func() {
 		if err := web.Start(webAddr, cfg.Server.SSHPort); err != nil {
-			log.Printf("Web server error: %v", err)
+			slog.Error("web server error", "error", err)
 		}
 	}()
 
-	log.Printf("Catacombs server starting — SSH :%d, Web :%d", cfg.Server.SSHPort, cfg.Server.HTTPPort)
+	slog.Info("server starting", "ssh_port", cfg.Server.SSHPort, "http_port", cfg.Server.HTTPPort)
 	if err := server.Start(sshAddr, lobby, db); err != nil {
 		log.Fatal(err)
 	}