feat(hunt): track walking distance via GPS, show live locations on map

Add foreground-only GPS distance tracking for hunts

prisma/schema.prisma

@@ -33,6 +33,9 @@ model User {
   reviews     Review[]
 
   uploadedFiles File[]
+
+  trackPoints TrackPoint[]
+  userTracks  UserTrack[]
 }
 
 enum UserRole {
@@ -80,6 +83,7 @@ model Hunt {
   revealQuests  Boolean   @default(false)
   revealAnswers Boolean   @default(false)
   public        Boolean   @default(true)
+  trackDistance Boolean   @default(false)
 
   creator   User @relation(fields: [creatorId], references: [id], onUpdate: Cascade, onDelete: Cascade)
   creatorId Int
@@ -98,6 +102,9 @@ model Hunt {
 
   oldFiles File[] @relation("OldHuntFiles")
 
+  trackPoints TrackPoint[]
+  userTracks  UserTrack[]
+
   @@index([creatorId])
 }
 
@@ -255,3 +262,41 @@ model Review {
   createdAt DateTime @default(now()) @db.Timestamptz(3)
   updatedAt DateTime @updatedAt @db.Timestamptz(3)
 }
+
+/// A single raw GPS fix streamed by the client while tracking is active.
+/// All points are retained (for future map features); distance is derived
+/// server-side and stored on UserTrack.
+model TrackPoint {
+  id  Int     @id @default(autoincrement())
+  lat Decimal @db.Decimal(10, 8)
+  lon Decimal @db.Decimal(10, 8)
+  /// Reported accuracy in meters, if the device provided one.
+  accuracy   Float?
+  recordedAt DateTime @db.Timestamptz(3)
+  createdAt  DateTime @default(now()) @db.Timestamptz(3)
+
+  user   User @relation(fields: [userId], references: [id], onUpdate: Cascade, onDelete: Cascade)
+  userId Int
+
+  hunt   Hunt @relation(fields: [huntId], references: [id], onUpdate: Cascade, onDelete: Cascade)
+  huntId Int
+
+  @@index([userId, huntId, recordedAt])
+}
+
+/// Per-user, per-hunt aggregate of the derived walking distance.
+/// Recomputed idempotently from all of the user's TrackPoints on each batch.
+model UserTrack {
+  id             Int       @id @default(autoincrement())
+  distanceMeters Int       @default(0)
+  lastFixAt      DateTime? @db.Timestamptz(3)
+  updatedAt      DateTime  @updatedAt @db.Timestamptz(3)
+
+  user   User @relation(fields: [userId], references: [id], onUpdate: Cascade, onDelete: Cascade)
+  userId Int
+
+  hunt   Hunt @relation(fields: [huntId], references: [id], onUpdate: Cascade, onDelete: Cascade)
+  huntId Int
+
+  @@unique([userId, huntId])
+}