feat: implement admin action APIs for comment and profile moderation

Added full API implementation for admin action buttons in the report
management interface:

Backend Changes:
- Created new /api/comments routes for admin-only comment operations
- Added PUT /api/comments/:id for admin comment editing
- Added DELETE /api/comments/:id for admin comment deletion
- Added POST /api/users/:id/make-private for admin profile privacy control
- All endpoints protected with adminGuard and csrfProtection
- Proper audit logging for all admin actions
- Added onDelete: Cascade to CommentReport relation for safe comment deletion

Frontend Changes:
- Added adminUpdateComment() and adminDeleteComment() to CommentsService
- Added makeProfilePrivate() to UserService
- Integrated API calls into admin-reports component methods
- editComment() now updates comment via API and refreshes report list
- deleteComment() now deletes comment via API and refreshes report list
- makeProfilePrivate() now updates profile privacy via API
- editProfile() navigates using ObjectId instead of Discord username
- All actions show success/error toasts and close modals on completion

The admin interface now has full working moderation capabilities for both
comment and profile reports.

api/prisma/schema.prisma

@@ -376,7 +376,7 @@ model ProfileReport {
 model CommentReport {
   id              String        @id @default(auto()) @map("_id") @db.ObjectId
   reportedCommentId String      @db.ObjectId
-  reportedComment Comment       @relation(fields: [reportedCommentId], references: [id])
+  reportedComment Comment       @relation(fields: [reportedCommentId], references: [id], onDelete: Cascade)
   reporterId      String        @db.ObjectId
   reporter        User          @relation("CommentReporter", fields: [reporterId], references: [id])
   reason          ReportReason