fix: add missing cmd/server/main.go and fix .gitignore

The .gitignore pattern "server" was matching cmd/server/ directory,
preventing main.go from being tracked. Anchored binary patterns to
repo root with leading slash.

cmd/server/main.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"log"
+	"net/http"
+	"os"
+
+	"mgit.msbls.de/m/patholo/internal/handlers"
+)
+
+func main() {
+	port := os.Getenv("PORT")
+	if port == "" {
+		port = "8080"
+	}
+
+	mux := http.NewServeMux()
+	handlers.Register(mux)
+
+	log.Printf("patholo server starting on :%s", port)
+	if err := http.ListenAndServe(":"+port, mux); err != nil {
+		log.Fatal(err)
+	}
+}