(bugfix) Add SSH private key file upload

Allow SSH credentials to be created from an uploaded private key file
as an alternative to pasting the key into a textarea.

Use multipart form handling in the credential views so server-side
keys can be imported without copy/paste wrapping or formatting damage.

Cover the upload path with a view test while keeping existing pasted
key validation behavior intact.

src/pobsync_backend/tests/test_views.py

@@ -6,6 +6,7 @@ from tempfile import TemporaryDirectory
 from unittest.mock import patch
 
 from django.contrib.auth import get_user_model
+from django.core.files.uploadedfile import SimpleUploadedFile
 from django.test import TestCase, override_settings
 from django.urls import reverse
 
@@ -117,6 +118,29 @@ class ViewTests(TestCase):
         self.assertEqual(credential.private_key, "PRIVATE KEY\n")
         self.assertEqual(credential.public_key, "DERIVED PUBLIC KEY")
 
+    def test_ssh_credentials_view_creates_key_from_uploaded_file(self) -> None:
+        self.client.force_login(self.staff_user)
+        uploaded_key = SimpleUploadedFile("id_ed25519", b"UPLOADED PRIVATE KEY\n", content_type="text/plain")
+
+        with patch("pobsync_backend.forms.validate_ssh_private_key", return_value="DERIVED PUBLIC KEY"):
+            response = self.client.post(
+                reverse("create_ssh_credential"),
+                {
+                    "name": "backup-key",
+                    "private_key_file": uploaded_key,
+                    "private_key": "",
+                    "public_key": "",
+                    "known_hosts": "",
+                    "notes": "uploaded",
+                },
+                follow=True,
+            )
+
+        self.assertRedirects(response, reverse("ssh_credentials"))
+        credential = SshCredential.objects.get(name="backup-key")
+        self.assertEqual(credential.private_key, "UPLOADED PRIVATE KEY\n")
+        self.assertEqual(credential.public_key, "DERIVED PUBLIC KEY")
+
     def test_ssh_credentials_view_rejects_invalid_key(self) -> None:
         self.client.force_login(self.staff_user)