feat(trips): trip tracking with analytics, tag conversion, and transaction assignment

Adds trips table usage across API and UI: trip CRUD, per-trip analytics
(category/daily/merchant/tag/participant breakdowns), tag-to-trip
conversion, trip assignment via transaction overrides, and trip filter
in the transactions view. Recovered from working tree after local git
corruption; feature was already live via host-context Docker builds.

prisma/schema.prisma

@@ -7,6 +7,19 @@ datasource db {
   provider = "postgresql"
 }
 
+model trips {
+  id          Int                     @id @default(autoincrement())
+  owner_id    Int
+  name        String
+  description String?
+  start_date  DateTime?               @db.Date
+  end_date    DateTime?               @db.Date
+  color       String                  @default("#6366f1")
+  archived    Boolean                 @default(false)
+  created_at  DateTime                @default(now())
+  overrides   transaction_overrides[]
+}
+
 model transaction_overrides {
   id                  Int       @id @default(autoincrement())
   transaction_id      Int       @unique
@@ -15,6 +28,8 @@ model transaction_overrides {
   notes               String?
   my_share_percent    Decimal?  @db.Decimal(5, 2)
   updated_at          DateTime  @default(now()) @updatedAt
+  trip_id             Int?
+  trip                trips?    @relation(fields: [trip_id], references: [id], onDelete: SetNull)
 }
 
 model participants {