(feature) Add host config editing view

Add a staff-only Django form for editing operational host settings while keeping
host identity stable. Support address, enablement, SSH/source overrides,
include/exclude lists, rsync extra args, and retention settings using the same
SQL-backed HostConfig model consumed by backup and scheduler flows.

Parse newline-separated list fields into JSON lists, preserve nullable
excludes_replace semantics, and cover rendering plus update behavior with view
tests.

src/pobsync_backend/tests/test_views.py

@@ -68,6 +68,7 @@ class ViewTests(TestCase):
         self.assertContains(response, "20260519-021500Z__ABCDEFGH")
         self.assertContains(response, "Discover snapshots")
         self.assertContains(response, "Edit schedule")
+        self.assertContains(response, "Edit config")
 
     def test_host_detail_returns_404_for_unknown_host(self) -> None:
         self.client.force_login(self.staff_user)
@@ -231,6 +232,92 @@ class ViewTests(TestCase):
         self.assertContains(response, "cron expression must have exactly 5 fields")
         self.assertFalse(ScheduleConfig.objects.filter(host=host).exists())
 
+    def test_host_config_form_renders_existing_values(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(
+            host="web-01",
+            address="web-01.example.test",
+            includes=["/srv"],
+            excludes_add=["*.tmp"],
+            rsync_extra_args=["--numeric-ids"],
+        )
+
+        response = self.client.get(reverse("edit_host_config", args=[host.host]))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "Config: web-01")
+        self.assertContains(response, "web-01.example.test")
+        self.assertContains(response, "/srv")
+        self.assertContains(response, "*.tmp")
+        self.assertContains(response, "--numeric-ids")
+
+    def test_host_config_form_updates_host_config(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="old.example.test")
+
+        response = self.client.post(
+            reverse("edit_host_config", args=[host.host]),
+            {
+                "address": "new.example.test",
+                "enabled": "on",
+                "ssh_user": "backup",
+                "ssh_port": "2222",
+                "source_root": "/srv",
+                "includes": "/srv/www\n/srv/db",
+                "excludes_add": "*.tmp\ncache/",
+                "excludes_replace": "",
+                "rsync_extra_args": "--numeric-ids\n--delete",
+                "retention_daily": "7",
+                "retention_weekly": "4",
+                "retention_monthly": "2",
+                "retention_yearly": "1",
+            },
+            follow=True,
+        )
+
+        self.assertRedirects(response, reverse("host_detail", args=[host.host]))
+        self.assertContains(response, "Host config saved for web-01.")
+        host.refresh_from_db()
+        self.assertEqual(host.address, "new.example.test")
+        self.assertEqual(host.ssh_user, "backup")
+        self.assertEqual(host.ssh_port, 2222)
+        self.assertEqual(host.source_root, "/srv")
+        self.assertEqual(host.includes, ["/srv/www", "/srv/db"])
+        self.assertEqual(host.excludes_add, ["*.tmp", "cache/"])
+        self.assertIsNone(host.excludes_replace)
+        self.assertEqual(host.rsync_extra_args, ["--numeric-ids", "--delete"])
+        self.assertEqual(host.retention_daily, 7)
+        self.assertEqual(host.retention_yearly, 1)
+
+    def test_host_config_form_can_replace_global_excludes(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+
+        response = self.client.post(
+            reverse("edit_host_config", args=[host.host]),
+            {
+                "address": host.address,
+                "ssh_user": "",
+                "ssh_port": "",
+                "source_root": "",
+                "includes": "",
+                "excludes_add": "",
+                "excludes_replace": "*.cache\nnode_modules/",
+                "rsync_extra_args": "",
+                "retention_daily": "14",
+                "retention_weekly": "8",
+                "retention_monthly": "12",
+                "retention_yearly": "0",
+            },
+            follow=True,
+        )
+
+        self.assertRedirects(response, reverse("host_detail", args=[host.host]))
+        host.refresh_from_db()
+        self.assertFalse(host.enabled)
+        self.assertEqual(host.excludes_add, [])
+        self.assertEqual(host.excludes_replace, ["*.cache", "node_modules/"])
+
     def _snapshot(self, host: HostConfig, dirname: str) -> SnapshotRecord:
         started_at = datetime.strptime(dirname.split("__", 1)[0], "%Y%m%d-%H%M%SZ").replace(tzinfo=timezone.utc)
         return SnapshotRecord.objects.create(