Add svelte-heros icon library

- Install svelte-heros for consistent Heroicons usage
- Replace inline SVGs for password toggle with Eye/EyeOff icons
- Fix USE_EMBEDDED mode to serve frontend from filesystem

backend/cmd/server/frontend.go

@@ -4,15 +4,22 @@ import (
 	"embed"
 	"io/fs"
 	"net/http"
+	"os"
 )
 
 //go:embed all:embed
 var Files embed.FS
 
-func FrontendFileSystem() http.FileSystem {
-	return http.FS(Files)
+func FrontendFileSystem() (http.FileSystem, string) {
+	if os.Getenv("USE_EMBEDDED") == "false" {
+		return http.Dir("../frontend/build"), ""
+	}
+	return http.FS(Files), "embed/"
 }
 
 func FrontendFS() fs.FS {
+	if os.Getenv("USE_EMBEDDED") == "false" {
+		return os.DirFS("../frontend/build")
+	}
 	return Files
 }