fix index path multiple fallbacks

internal/handler/index.go

@@ -3,6 +3,8 @@ package handler
 import (
 "net/http"
 "os"
+"path/filepath"
+"runtime"
 )
 
 func HandleIndex(w http.ResponseWriter, r *http.Request) {
@@ -10,11 +12,19 @@ if r.URL.Path != "/" {
 http.NotFound(w, r)
 return
 }
-content, err := os.ReadFile("/app/static/index.html")
+_, filename, _, _ := runtime.Caller(0)
+dir := filepath.Join(filepath.Dir(filename), "..", "..", "static", "index.html")
+content, err := os.ReadFile(dir)
 if err != nil {
-http.Error(w, "Page not found", 404)
+content, err = os.ReadFile("static/index.html")
+if err != nil {
+content, err = os.ReadFile("/app/static/index.html")
+if err != nil {
+http.Error(w, "Page not found: "+err.Error(), 404)
 return
 }
+}
+}
 w.Header().Set("Content-Type", "text/html; charset=utf-8")
 w.Write(content)
 }