Adopt SummerCMS v0.1.1 admin features

Datepickers on native time.Time / lagoon.Date fields, file uploads on
materials, readings and class sessions managed from the course form
(course_id made nullable).

lang/en/lang.yaml

@@ -23,8 +23,6 @@ common:
     sort_order: Sort order
     created_at: Created
     none: — none —
-    date_comment: A date in the YYYY-MM-DD form, such as 2026-10-03.
-    datetime_comment: Date and time in Polish time, such as 2026-10-03 08:00.
 forms:
     wyklad: Lecture
     cwiczenia: Tutorial
@@ -32,6 +30,8 @@ forms:
     seminarium: Seminar
     inne: Other
 courses:
+    readings: Readings
+    sessions: Class sessions
     title: Courses
     form: Course
     name: Name
@@ -83,7 +83,8 @@ materials:
     body: Body (Markdown)
     body_comment: A note in Markdown.
     published_at: Published
-    published_at_comment: Leave empty for a draft that students do not see. Such as 2026-10-03 08:00.
+    files: Files
+    published_at_comment: Leave empty for a draft that students do not see.
     tags: Tags
 material_types:
     pdf: PDF

lang/pl/lang.yaml

@@ -23,8 +23,6 @@ common:
     sort_order: Kolejność
     created_at: Utworzono
     none: — brak —
-    date_comment: Data w formacie RRRR-MM-DD, np. 2026-10-03.
-    datetime_comment: Data i godzina czasu polskiego, np. 2026-10-03 08:00.
 forms:
     wyklad: Wykład
     cwiczenia: Ćwiczenia
@@ -32,6 +30,8 @@ forms:
     seminarium: Seminarium
     inne: Inne
 courses:
+    readings: Lektury
+    sessions: Zajęcia
     title: Przedmioty
     form: Przedmiot
     name: Nazwa
@@ -83,7 +83,8 @@ materials:
     body: Treść (Markdown)
     body_comment: Notatka w Markdownie.
     published_at: Opublikowano
-    published_at_comment: Puste pole to szkic, niewidoczny dla studentów. Np. 2026-10-03 08:00.
+    files: Pliki
+    published_at_comment: Puste pole to szkic, niewidoczny dla studentów.
     tags: Tagi
 material_types:
     pdf: PDF