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

frontend/src/lib/types.ts

@@ -33,10 +33,11 @@ export interface User {
 export interface Certificate {
   id: number;
   userId: number;
-  publicId: string;
+  publicId?: string;
   fullName: string;
   issuedAt: string;
   revokedAt?: string;
+  status: "pending" | "issued";
 }
 
 export type PhysicalOrderStatus = "requested" | "paid" | "shipped" | "cancelled";
@@ -91,6 +92,7 @@ export interface Lesson {
   sortOrder: number;
   xpReward: number;
   isActive: boolean;
+  isPublished: boolean;
 }
 
 export interface Chapter {
@@ -99,6 +101,7 @@ export interface Chapter {
   description: string;
   icon: string;
   sortOrder: number;
+  isPublished: boolean;
 }
 
 export interface TreeLesson {
@@ -122,6 +125,9 @@ export interface TreeChapter extends Chapter {
 
 export interface TreeData {
   chapters: TreeChapter[];
+  totalLessons: number;
+  completedLessons: number;
+  progressPct: number;
   me: { xp: number; streak: number; hearts: number; isLocked: boolean; role: Role };
 }
 
@@ -246,12 +252,15 @@ export interface Conversation {
   archived: boolean;
 }
 
+export type LeaderboardTier = "champion" | "gold" | "silver" | "bronze";
+
 export interface LeaderboardEntry {
   userId: number;
   name: string;
   email: string;
   xp: number;
   rank: number;
+  tier: LeaderboardTier;
   avatarVariant?: "marble" | "beam" | "pixel" | "sunset" | "ring" | "bauhaus";
   avatarPalette?: string;
   avatarPhoto?: string;
@@ -260,7 +269,8 @@ export interface LeaderboardEntry {
 export interface LeaderboardData {
   week: string;
   entries: LeaderboardEntry[];
-  me: { rank: number; xp: number; streak: number };
+  totalParticipants: number;
+  me: { rank: number; xp: number; streak: number; tier: LeaderboardTier };
 }
 
 export interface NotificationPrefs {