(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/views.py

@@ -8,7 +8,7 @@ from django.views.decorators.http import require_POST
 
 from pobsync.errors import ConfigError
 
-from .forms import ScheduleConfigForm
+from .forms import HostConfigForm, ScheduleConfigForm
 from .models import BackupRun, HostConfig, ScheduleConfig, SnapshotRecord
 from .retention import run_sql_retention_plan
 from .snapshot_discovery import discover_snapshots
@@ -96,6 +96,28 @@ def host_retention_plan(request, host: str):
     return render(request, "pobsync_backend/retention_plan.html", context)
 
 
+@staff_member_required
+def edit_host_config(request, host: str):
+    host_config = get_object_or_404(HostConfig, host=host)
+    if request.method == "POST":
+        form = HostConfigForm(request.POST, instance=host_config)
+        if form.is_valid():
+            form.save()
+            messages.success(request, f"Host config saved for {host_config.host}.")
+            return redirect("host_detail", host=host_config.host)
+    else:
+        form = HostConfigForm(instance=host_config)
+
+    return render(
+        request,
+        "pobsync_backend/host_form.html",
+        {
+            "host": host_config,
+            "form": form,
+        },
+    )
+
+
 @staff_member_required
 def edit_host_schedule(request, host: str):
     host_config = get_object_or_404(HostConfig, host=host)