feat: Django admin page for CourseArchiveStatus

Expose the sample plugin's one model in the LMS/CMS admin so operators
can inspect and manage records without custom tooling, and so the
sample demonstrates the standard ModelAdmin pattern alongside the
other plugin interfaces.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kdmccormick

backend-plugin-sample/src/openedx_plugin_sample/admin.py

@@ -0,0 +1,55 @@
+"""
+Django admin configuration for openedx_plugin_sample.
+
+This module demonstrates how to expose plugin models in the Django admin
+site provided by Open edX (LMS and CMS each have their own admin under
+``/admin/``). Defining a ``ModelAdmin`` for each model gives operators a
+ready-made UI to inspect and manage plugin data without needing custom
+tooling.
+
+Django Documentation:
+- ModelAdmin: https://docs.djangoproject.com/en/stable/ref/contrib/admin/
+"""
+
+from django.contrib import admin
+
+from openedx_plugin_sample.models import CourseArchiveStatus
+
+
+@admin.register(CourseArchiveStatus)
+class CourseArchiveStatusAdmin(admin.ModelAdmin):
+    """
+    Admin configuration for the CourseArchiveStatus model.
+    """
+
+    list_display = (
+        "course_key",
+        "user",
+        "is_archived",
+        "archive_date",
+        "updated_at",
+    )
+    list_filter = ("is_archived",)
+    # Search by the related CourseRun's course_key and the user's username/email.
+    search_fields = (
+        "course_run__course_key",
+        "user__username",
+        "user__email",
+    )
+    # FKs use raw id widgets (lookup popup) rather than a <select>, since the
+    # CourseRun and User tables can have many thousands of rows on a real
+    # Open edX deployment.
+    raw_id_fields = ("course_run", "user")
+    readonly_fields = ("created_at", "updated_at")
+    ordering = ("-updated_at",)
+
+    @admin.display(description="Course key", ordering="course_run__course_key")
+    def course_key(self, obj: CourseArchiveStatus) -> str:
+        """
+        Show the course's course_key string in list_display.
+
+        We never expose CourseRun's internal integer PK in the admin; the
+        course_key (e.g. "course-v1:edX+DemoX+Demo_Course") is the identifier
+        operators recognize.
+        """
+        return str(obj.course_run.course_key)