perbaikan

Pada script Anda sebenarnya sudah hampir benar. Yang perlu ditambahkan adalah:

1. Preview foto harus memiliki id.
2. Saat file dipilih, tampilkan preview.
3. Upload otomatis menggunakan AJAX.
4. Simpan path gambar ke database.
5. Tidak perlu tombol upload.

1. Ubah bagian foto menjadi:

<div class="profile-wrapper">

    <img src="<?=$row['gambar'];?>"
         id="preview"
         class="profile-photo">

    <button type="button"
            class="camera-btn"
            onclick="document.getElementById('foto').click()">

        <i class="bi bi-camera-fill"></i>

    </button>

    <input type="file"
           id="foto"
           name="foto"
           accept="image/*"
           style="display:none;">

    <input type="hidden"
           id="id_siswa"
           value="<?=$idSiswa;?>">

</div>

<div id="uploadStatus"
     class="small mt-2 text-secondary">
</div>

---

2. Tambahkan script sebelum </body>

<script>

$('#foto').on('change', function(){

    let file = this.files[0];

    if(!file){
        return;
    }

    /*
    |--------------------------------------------------------------------------
    | Preview Langsung
    |--------------------------------------------------------------------------
    */
    let previewUrl = URL.createObjectURL(file);

    $('#preview').attr('src', previewUrl);

    $('#uploadStatus').html(
        '<span class="text-primary">Mengupload foto...</span>'
    );

    /*
    |--------------------------------------------------------------------------
    | Upload Otomatis
    |--------------------------------------------------------------------------
    */
    let formData = new FormData();

    formData.append('foto', file);
    formData.append(
        'id_siswa',
        $('#id_siswa').val()
    );

    $.ajax({

        url:'upload_foto_siswa.php',

        type:'POST',

        data:formData,

        contentType:false,

        processData:false,

        success:function(res){

            try{

                let data = JSON.parse(res);

                if(data.success){

                    $('#preview').attr(
                        'src',
                        data.url + '?t=' + Date.now()
                    );

                    $('#uploadStatus').html(
                        '<span class="text-success">✓ Foto berhasil diperbarui</span>'
                    );

                }else{

                    $('#uploadStatus').html(
                        '<span class="text-danger">Upload gagal</span>'
                    );

                }

            }catch(e){

                $('#uploadStatus').html(
                    '<span class="text-danger">Terjadi kesalahan</span>'
                );

            }

        }

    });

});

</script>

---

3. Buat file upload_foto_siswa.php

<?php

include "koneksi.php";

$response = [
    'success' => false
];

if(
    isset($_FILES['foto']) &&
    isset($_POST['id_siswa'])
){

    $id_siswa = $_POST['id_siswa'];

    $folder = "uploads/siswa/";

    if(!is_dir($folder)){
        mkdir($folder,0777,true);
    }

    $ext = strtolower(
        pathinfo(
            $_FILES['foto']['name'],
            PATHINFO_EXTENSION
        )
    );

    $namaFile =
        "siswa_" .
        $id_siswa .
        "_" .
        time() .
        "." .
        $ext;

    $path = $folder . $namaFile;

    if(
        move_uploaded_file(
            $_FILES['foto']['tmp_name'],
            $path
        )
    ){

        mysqli_query(
            $conn,
            "UPDATE tbl_siswa
             SET gambar='$path'
             WHERE id='$id_siswa'"
        );

        $response['success'] = true;
        $response['url'] = $path;

    }

}

echo json_encode($response);

---

Bonus (lebih elegan)

Tambahkan CSS berikut:

.camera-btn{
    position:absolute;
    right:5px;
    bottom:5px;
    width:42px;
    height:42px;
    border:none;
    border-radius:50%;
    background:#0d6efd;
    color:#fff;
    box-shadow:0 4px 10px rgba(0,0,0,.2);
}

.profile-wrapper{
    position:relative;
    width:140px;
    margin:auto;
}

Hasilnya akan seperti WhatsApp/Instagram:

• Klik ikon kamera 📷
• Pilih foto
• Preview langsung berubah
• Upload otomatis ke server
• Database tbl_siswa.gambar langsung terupdate
• Tidak ada tombol upload lagi.