feat: implement comprehensive achievement system with 62 achievements

Adds a complete achievement system with gamification features across all user interactions.

**Database & Types:**
- Add UserAchievement model to track user progress and earned achievements
- Add achievement-related fields to User model (achievementPoints, currentStreak, lastStreakCheck)
- Add ACHIEVEMENT_UNLOCKED audit action type
- Define 62 achievements as TypeScript constants across 5 categories

**Achievement Categories:**
- Suggestions (15): First suggestion through ultimate curator milestones
- Likes (12): First like through legendary fan milestones
- Comments (12): First comment through review legend milestones
- Engagement (15): Login streaks and total activity tracking
- Reports (8): Valid reports and accuracy tracking

**Backend Implementation:**
- Create AchievementService with comprehensive checking logic
- Add achievement route with 6 API endpoints
- Integrate achievement checking into all user interaction points:
  - Suggestions (create + accept)
  - Likes (toggle)
  - Comments (all 6 media types)
  - Login streaks
  - Reports (profile + comment)
- Update UserService to include achievement points in profiles

**Frontend Implementation:**
- Create AchievementService for API communication
- Create achievements page showing all 62 achievements with:
  - Category filtering (All, Suggestions, Likes, Comments, Engagement, Reports)
  - Tier-based styling (Bronze, Silver, Gold, Platinum, Diamond)
  - Progress indicators for in-progress achievements
  - Earned date display for completed achievements
- Add "Recent Achievements" section to user profiles
- Add "🏆 Achievements" link to header navigation
- Only show "View All" link on own profile

**Technical Features:**
- Real-time achievement checking on user actions
- Progress tracking to avoid recalculation
- Points system for gamification
- Tier-based gradient styling
- Leaderboard-ready architecture

Resolves #48

Co-Authored-By: Hikari <hikari@nhcarrigan.com>

apps/frontend/src/app/services/user.service.ts

@@ -24,6 +24,7 @@ export interface UserProfileResponse {
   linkedin?: string;
   twitch?: string;
   youtube?: string;
+  achievementPoints: number;
   badges: {
     isStaff: boolean;
     isMod: boolean;