feat: add the BM management MCP tools

- 28 typed tools over /api/v1/bm: list, show, create and update for
  courses and meetings, plus delete for class sessions, readings,
  deadlines and materials (save upserts on title and course)
- inputs mirror Fillable and Rules; enums, lengths and date formats in
  the field descriptions; no seed, me or dry_run tool
- materials accept meeting_id (absent keeps, null clears, must exist)
  and the managed material JSON shows it
- README: MCP tools section

controllers/api/manage.go

@@ -141,6 +141,7 @@ type managedMaterialJSON struct {
 	ID          uint       `json:"id"`
 	CourseID    *uint      `json:"course_id"`
 	Course      *courseRef `json:"course"`
+	MeetingID   *uint      `json:"meeting_id"`
 	Title       string     `json:"title"`
 	Type        string     `json:"type"`
 	Body        *string    `json:"body"`
@@ -152,7 +153,7 @@ type managedMaterialJSON struct {
 
 func newManagedMaterialJSON(m models.Material) managedMaterialJSON {
 	out := managedMaterialJSON{
-		ID: m.ID, CourseID: m.CourseID, Course: newCourseRef(m.Course), Title: m.Title, Type: m.Type,
+		ID: m.ID, CourseID: m.CourseID, Course: newCourseRef(m.Course), MeetingID: m.MeetingID, Title: m.Title, Type: m.Type,
 		Body: m.Body, Source: m.Source, URL: m.URL, Tags: newTagsJSON(m.Tags),
 	}
 	if m.PublishedAt != nil {
@@ -185,6 +186,7 @@ func (h *Handlers) ManagedMaterials(w http.ResponseWriter, r *http.Request) {
 // materialInput is the body of POST /materials and PUT /materials/{id}.
 type materialInput struct {
 	CourseID    *uint     `json:"course_id"`
+	MeetingID   *uint     `json:"meeting_id"`
 	Title       string    `json:"title"`
 	Type        string    `json:"type"`
 	Body        *string   `json:"body"`
@@ -200,8 +202,12 @@ type materialDraft struct {
 	// hasPublishedAt tells a sent published_at (null included) from an
 	// absent one.
 	hasPublishedAt bool
-	publishedAt    *time.Time
-	tags           []models.Tag
+	// hasMeetingID tells a sent meeting_id (null included) from an absent
+	// one: absent keeps the stored meeting, so scripts that never send it
+	// keep working.
+	hasMeetingID bool
+	publishedAt  *time.Time
+	tags         []models.Tag
 }
 
 // readMaterial decodes and validates the body of POST /materials and
@@ -222,6 +228,7 @@ func (h *Handlers) readMaterial(w http.ResponseWriter, r *http.Request, db *gorm
 	var keys map[string]json.RawMessage
 	_ = json.Unmarshal(raw, &keys)
 	_, d.hasPublishedAt = keys["published_at"]
+	_, d.hasMeetingID = keys["meeting_id"]
 
 	in := &d.in
 	in.Title = strings.TrimSpace(in.Title)
@@ -268,6 +275,16 @@ func (h *Handlers) readMaterial(w http.ResponseWriter, r *http.Request, db *gorm
 			errs["course_id"] = []string{"The selected course_id is invalid."}
 		}
 	}
+	if in.MeetingID != nil {
+		var n int64
+		if err := db.Model(&models.Meeting{}).Where("id = ?", *in.MeetingID).Count(&n).Error; err != nil {
+			writeOpaque500(w)
+			return d, false
+		}
+		if n == 0 {
+			errs["meeting_id"] = []string{"The selected meeting_id is invalid."}
+		}
+	}
 	if len(errs) > 0 {
 		writeValidation(w, errs)
 		return d, false
@@ -287,19 +304,23 @@ func (d materialDraft) identity(q *gorm.DB) *gorm.DB {
 
 // apply writes the draft onto m inside tx. published_at: absent publishes
 // a new material now and keeps an existing one as it is; null makes a
-// draft; otherwise the sent time. tags: absent keeps them; otherwise the
-// list replaces them, and unknown tags are created.
+// draft; otherwise the sent time. meeting_id: absent keeps it; null clears
+// it. tags: absent keeps them; otherwise the list replaces them, and unknown
+// tags are created.
 func (d materialDraft) apply(tx *gorm.DB, m *models.Material, created bool, now time.Time) error {
 	in := d.in
 	m.CourseID, m.Title, m.Type = in.CourseID, in.Title, in.Type
 	m.Body, m.Source, m.URL = in.Body, in.Source, in.URL
+	if d.hasMeetingID {
+		m.MeetingID = in.MeetingID
+	}
 	switch {
 	case d.hasPublishedAt:
 		m.PublishedAt = d.publishedAt
 	case created:
 		m.PublishedAt = &now
 	}
-	if err := tx.Omit("Course", "Tags").Save(m).Error; err != nil {
+	if err := tx.Omit("Course", "Meeting", "Tags").Save(m).Error; err != nil {
 		return err
 	}
 	if in.Tags == nil {