feat: add trip preference overrides with precedence resolution

backend/apps/api/src/trips/trip-preference-overrides.controller.ts

@@ -0,0 +1,59 @@
+import {
+  Body,
+  Controller,
+  Delete,
+  ForbiddenException,
+  Get,
+  Param,
+  Put,
+  UseGuards,
+} from '@nestjs/common';
+import { OidcAuthGuard } from '../../../../libs/auth/src';
+import type { AuthenticatedUser } from '../../../../libs/auth/src';
+import {
+  TripMembershipGuard,
+  TripPreferenceOverridesService,
+} from '../../../../libs/trips/src';
+import type {
+  TripMemberRole,
+  TripPreferenceOverride,
+  UpsertPreferenceOverrideDto,
+} from '../../../../libs/trips/src';
+import { CurrentUser } from '../auth/current-user.decorator';
+import { CurrentTripRole } from './current-trip-role.decorator';
+
+@Controller('trips/:tripId/preference-overrides')
+@UseGuards(OidcAuthGuard, TripMembershipGuard)
+export class TripPreferenceOverridesController {
+  constructor(private readonly service: TripPreferenceOverridesService) {}
+
+  @Get()
+  list(@Param('tripId') tripId: string): Promise<TripPreferenceOverride[]> {
+    return this.service.listOverrides(tripId);
+  }
+
+  @Put()
+  async upsert(
+    @Param('tripId') tripId: string,
+    @CurrentUser() currentUser: AuthenticatedUser,
+    @CurrentTripRole() role: TripMemberRole,
+    @Body() dto: UpsertPreferenceOverrideDto,
+  ): Promise<TripPreferenceOverride> {
+    const isOwnUserOverride =
+      dto.subject.type === 'USER' && dto.subject.userId === currentUser.id;
+    if (role !== 'OWNER' && !isOwnUserOverride) {
+      throw new ForbiddenException(
+        'Only the trip owner may set preference overrides for other members or travelers',
+      );
+    }
+    return this.service.upsertOverride(tripId, dto.subject, dto.overrides);
+  }
+
+  @Delete(':overrideId')
+  remove(
+    @Param('tripId') tripId: string,
+    @Param('overrideId') overrideId: string,
+  ): Promise<void> {
+    return this.service.removeOverride(tripId, overrideId);
+  }
+}