feat: implement 8 features across full stack

- Leaderboard: rank-based percentile tiers (champion/gold/silver/bronze),
    deterministic tie-breaking (xp DESC, user_id ASC)
  - Mentor chat: md: breakpoints, safe-area-inset-bottom padding
  - Learning progress: server-side progressPct, curriculum expansion safety
  - Physical orders: hard-disabled with 410 Gone
  - Certificate approval: pending/issued flow, admin issue/revoke endpoints,
    certificate_requires_approval setting (migration 0031)
  - Draft/publish: is_published on lessons and chapters, admin publish UI
    (migration 0030)
  - Video panel: static thumbnails (no preload), client-side pagination
  - Rich editor: TipTap + tiptap-markdown for lesson descriptions,
    marked + DOMPurify for SafeMarkdown rendering

backend/internal/api/admin.go

@@ -575,6 +575,38 @@ func (s *Server) handleAdminDeleteLesson(w http.ResponseWriter, r *http.Request)
 	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
 }
 
+func (s *Server) handleAdminPublishLesson(w http.ResponseWriter, r *http.Request) {
+	id := routeID(r, "id")
+	var body struct {
+		Publish bool `json:"publish"`
+	}
+	if err := bodyJSON(r, &body); err != nil {
+		writeErr(w, http.StatusBadRequest, "دادهٔ ارسالی نامعتبر است")
+		return
+	}
+	if err := s.store.PublishLesson(r.Context(), id, body.Publish); err != nil {
+		writeErr(w, http.StatusInternalServerError, "به‌روزرسانی وضعیت درس ممکن نشد")
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
+}
+
+func (s *Server) handleAdminPublishChapter(w http.ResponseWriter, r *http.Request) {
+	id := routeID(r, "id")
+	var body struct {
+		Publish bool `json:"publish"`
+	}
+	if err := bodyJSON(r, &body); err != nil {
+		writeErr(w, http.StatusBadRequest, "دادهٔ ارسالی نامعتبر است")
+		return
+	}
+	if err := s.store.PublishChapter(r.Context(), id, body.Publish); err != nil {
+		writeErr(w, http.StatusInternalServerError, "به‌روزرسانی وضعیت فصل ممکن نشد")
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
+}
+
 // ---- questions ----
 
 func (s *Server) handleAdminListQuestions(w http.ResponseWriter, r *http.Request) {