Add 'Mark as Cleaned Up' functionality

- Add cleaned_at and cleaned_by_user_id fields to reports table
- Create database migration for cleanup tracking
- Add markAsCleaned backend endpoint and service method
- Add Mark as Cleaned Up button to ReportDetailModal
- Update types to include cleaned fields
- Add frontend handler to mark reports as cleaned

server/prisma/schema.prisma

@@ -25,6 +25,7 @@ model User {
   eventRegistrations EventRegistration[]
   organizedEvents    Event[]             @relation("EventOrganizer")
   reports            Report[]
+  cleanedReports     Report[]            @relation("CleanedByUser")
   verifications      Verification[]
 
   @@index([clerkId], map: "idx_clerk_id")
@@ -49,15 +50,20 @@ model Report {
   updatedAt             DateTime?                    @default(now()) @updatedAt @map("updated_at") @db.Timestamp(0)
   submittedAt           DateTime?                    @default(now()) @map("submitted_at") @db.Timestamp(0)
   verificationStatus    reports_verification_status? @default(pending) @map("verification_status")
+  cleanedAt             DateTime?                    @map("cleaned_at") @db.Timestamp(0)
+  cleanedByUserId       String?                      @map("cleaned_by_user_id") @db.VarChar(36)
   environmentalConcerns EnvironmentalConcern[]
   user                  User                         @relation(fields: [userId], references: [id], onDelete: Cascade, onUpdate: NoAction, map: "reports_ibfk_1")
+  cleanedByUser         User?                        @relation("CleanedByUser", fields: [cleanedByUserId], references: [id], onDelete: SetNull, onUpdate: NoAction, map: "reports_cleaned_by_fk")
   verifications         Verification[]
 
   @@index([createdAt], map: "idx_created_at")
+  @@index([cleanedAt], map: "idx_cleaned_at")
   @@index([latitude, longitude], map: "idx_lat_lng")
   @@index([litterType], map: "idx_litter_type")
   @@index([location(length: 32)], map: "idx_location")
   @@index([userId], map: "user_id")
+  @@index([cleanedByUserId], map: "cleaned_by_user_id")
   @@map("reports")
 }