feat: add GPS trip detection, history panel, and playback (#23)

Auto-detect trips from GPS data (5-min idle threshold), pre-compute
OSRM routes on trip completion, add trip history side panel with
toggleable trips, and animated trip playback with speed controls.

- Add GpsTrip model with TripStatus enum and migration
- Trip detection in syncPositions cron (start on movement, end on idle)
- Trip finalization with OSRM route matching and stats computation
- API endpoints: list/detail/active/merge/backfill trips
- Stats tab overhaul: trip list panel + map with colored polylines
- Trip playback: animated marker, progressive trail, 1x-16x speed
- Live map shows active trip trail instead of full day history
- Historical backfill from existing GPS location data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/prisma/schema.prisma

@@ -405,6 +405,7 @@ model GpsDevice {
 
   // Location history
   locationHistory   GpsLocationHistory[]
+  trips             GpsTrip[]
 
   createdAt         DateTime  @default(now())
   updatedAt         DateTime  @updatedAt
@@ -434,6 +435,45 @@ model GpsLocationHistory {
   @@index([timestamp]) // For cleanup job
 }
 
+enum TripStatus {
+  ACTIVE        // Currently in progress
+  COMPLETED     // Finished, OSRM route computed
+  PROCESSING    // OSRM computation in progress
+  FAILED        // OSRM computation failed
+}
+
+model GpsTrip {
+  id                String     @id @default(uuid())
+  deviceId          String
+  device            GpsDevice  @relation(fields: [deviceId], references: [id], onDelete: Cascade)
+
+  status            TripStatus @default(ACTIVE)
+
+  startTime         DateTime
+  endTime           DateTime?
+  startLatitude     Float
+  startLongitude    Float
+  endLatitude       Float?
+  endLongitude      Float?
+
+  // Pre-computed stats (filled on completion)
+  distanceMiles     Float?
+  durationSeconds   Int?
+  topSpeedMph       Float?
+  averageSpeedMph   Float?
+  pointCount        Int        @default(0)
+
+  // Pre-computed OSRM route (stored as JSON for instant display)
+  matchedRoute      Json?      // { coordinates: [lat,lng][], distance, duration, confidence }
+
+  createdAt         DateTime   @default(now())
+  updatedAt         DateTime   @updatedAt
+
+  @@map("gps_trips")
+  @@index([deviceId, startTime])
+  @@index([status])
+}
+
 model GpsSettings {
   id                    String   @id @default(uuid())