feat: materials by zjazd in the student API and admin

The material admin form gets the "Na zjazd" picker, every student
material JSON carries meeting_id, and GET /materials accepts meeting=
inside the published-only scope, so the Pulpit hero can list the
zjazd's materials next to its readings.

models/material.go

@@ -23,6 +23,8 @@ type Material struct {
 	ID          uint       `gorm:"column:id;primaryKey"`
 	CourseID    *uint      `gorm:"column:course_id"`
 	Course      *Course    `gorm:"foreignKey:CourseID"`
+	MeetingID   *uint      `gorm:"column:meeting_id"`
+	Meeting     *Meeting   `gorm:"foreignKey:MeetingID"`
 	Title       string     `gorm:"column:title"`
 	Type        string     `gorm:"column:type"`
 	Body        *string    `gorm:"column:body"`
@@ -43,7 +45,7 @@ func (Material) MorphName() string { return `Jz\Bm\Models\Material` }
 
 // Fillable lists the columns mass assignment may set.
 func (Material) Fillable() []string {
-	return []string{"course_id", "title", "type", "body", "source", "url", "published_at"}
+	return []string{"course_id", "meeting_id", "title", "type", "body", "source", "url", "published_at"}
 }
 
 // Rules are checked by the admin API on every save.

models/materials/fields.yaml

@@ -36,6 +36,13 @@ fields:
         label: jz.bm::lang.common.url
         type: text
         span: right
+    meeting:
+        label: jz.bm::lang.common.meeting
+        type: relation
+        nameFrom: number
+        span: left
+        emptyOption: jz.bm::lang.common.none
+        comment: jz.bm::lang.common.meeting_comment
     tags:
         label: jz.bm::lang.materials.tags
         type: relation