feat: Configure database with Prisma and MySQL spatial support (Task 22)

- Set up MySQL 8.0+ with spatial data support (POINT SRID 4326)
- Created Prisma schema with all models (User, Report, Event, etc.)
- Added Clerk authentication support (clerk_id field)
- Configured spatial indexes on location fields for performance
- Created database migrations and applied to MySQL
- Built spatial query utilities for geographical operations
- Added database connection singleton and health checks
- Created comprehensive documentation and test scripts

Requirements: 1.1, 2.1, 3.2, 4.1

server/prisma/schema.prisma

@@ -21,11 +21,13 @@ model User {
   notificationEmail  Boolean?            @default(true) @map("notification_email")
   notificationInApp  Boolean?            @default(true) @map("notification_in_app")
   areasOfInterest    Json?               @map("areas_of_interest")
+  clerkId            String?             @unique(map: "clerk_id") @map("clerk_id") @db.VarChar(255)
   eventRegistrations EventRegistration[]
   organizedEvents    Event[]             @relation("EventOrganizer")
   reports            Report[]
   verifications      Verification[]
 
+  @@index([clerkId], map: "idx_clerk_id")
   @@index([email], map: "idx_email")
   @@index([username], map: "idx_username")
   @@map("users")