feat(cache): implement Redis caching layer for hot-read endpoints

Add cache-aside pattern for listing detail, search results, market
analytics (4 endpoints), and user profile queries. Cache invalidation
on all write mutations. Prometheus cache_hit_total/cache_miss_total
metrics with resource labels.

- CacheService: getOrSet, invalidate, invalidateByPrefix (SCAN-based)
- TTLs: listing 5m, search 1m, market 30m, profile 10m
- All 230 tests passing (13 new cache tests + 6 updated handler tests)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/listings/application/commands/create-listing/create-listing.handler.ts

@@ -1,6 +1,7 @@
 import { CommandHandler, EventBus, type ICommandHandler } from '@nestjs/cqrs';
 import { Inject, BadRequestException } from '@nestjs/common';
 import { createId } from '@paralleldrive/cuid2';
+import { CacheService, CachePrefix } from '@modules/shared/infrastructure/cache.service';
 import { CreateListingCommand } from './create-listing.command';
 import { PROPERTY_REPOSITORY, type IPropertyRepository } from '../../../domain/repositories/property.repository';
 import { LISTING_REPOSITORY, type IListingRepository } from '../../../domain/repositories/listing.repository';
@@ -22,6 +23,7 @@ export class CreateListingHandler implements ICommandHandler<CreateListingComman
     @Inject(PROPERTY_REPOSITORY) private readonly propertyRepo: IPropertyRepository,
     @Inject(LISTING_REPOSITORY) private readonly listingRepo: IListingRepository,
     private readonly eventBus: EventBus,
+    private readonly cache: CacheService,
   ) {}
 
   async execute(command: CreateListingCommand): Promise<CreateListingResult> {
@@ -87,6 +89,8 @@ export class CreateListingHandler implements ICommandHandler<CreateListingComman
       this.eventBus.publish(event);
     }
 
+    await this.cache.invalidateByPrefix(CachePrefix.SEARCH);
+
     return {
       listingId,
       propertyId,

apps/api/src/modules/listings/application/commands/moderate-listing/moderate-listing.handler.ts

@@ -1,6 +1,7 @@
 import { CommandHandler, EventBus, type ICommandHandler } from '@nestjs/cqrs';
 import { Inject } from '@nestjs/common';
 import { NotFoundException } from '@modules/shared/domain/domain-exception';
+import { CacheService, CachePrefix } from '@modules/shared/infrastructure/cache.service';
 import { ModerateListingCommand } from './moderate-listing.command';
 import { LISTING_REPOSITORY, type IListingRepository } from '../../../domain/repositories/listing.repository';
 
@@ -9,6 +10,7 @@ export class ModerateListingHandler implements ICommandHandler<ModerateListingCo
   constructor(
     @Inject(LISTING_REPOSITORY) private readonly listingRepo: IListingRepository,
     private readonly eventBus: EventBus,
+    private readonly cache: CacheService,
   ) {}
 
   async execute(command: ModerateListingCommand): Promise<{ status: string }> {
@@ -34,6 +36,11 @@ export class ModerateListingHandler implements ICommandHandler<ModerateListingCo
       this.eventBus.publish(event);
     }
 
+    await Promise.all([
+      this.cache.invalidate(CacheService.buildKey(CachePrefix.LISTING, command.listingId)),
+      this.cache.invalidateByPrefix(CachePrefix.SEARCH),
+    ]);
+
     return { status: listing.status };
   }
 }

apps/api/src/modules/listings/application/commands/update-listing-status/update-listing-status.handler.ts

@@ -1,6 +1,7 @@
 import { CommandHandler, EventBus, type ICommandHandler } from '@nestjs/cqrs';
 import { Inject } from '@nestjs/common';
 import { NotFoundException } from '@modules/shared/domain/domain-exception';
+import { CacheService, CachePrefix } from '@modules/shared/infrastructure/cache.service';
 import { UpdateListingStatusCommand } from './update-listing-status.command';
 import { LISTING_REPOSITORY, type IListingRepository } from '../../../domain/repositories/listing.repository';
 
@@ -9,6 +10,7 @@ export class UpdateListingStatusHandler implements ICommandHandler<UpdateListing
   constructor(
     @Inject(LISTING_REPOSITORY) private readonly listingRepo: IListingRepository,
     private readonly eventBus: EventBus,
+    private readonly cache: CacheService,
   ) {}
 
   async execute(command: UpdateListingStatusCommand): Promise<{ status: string }> {
@@ -32,6 +34,11 @@ export class UpdateListingStatusHandler implements ICommandHandler<UpdateListing
       this.eventBus.publish(event);
     }
 
+    await Promise.all([
+      this.cache.invalidate(CacheService.buildKey(CachePrefix.LISTING, command.listingId)),
+      this.cache.invalidateByPrefix(CachePrefix.SEARCH),
+    ]);
+
     return { status: listing.status };
   }
 }

apps/api/src/modules/listings/application/queries/get-listing/get-listing.handler.ts

@@ -1,6 +1,7 @@
 import { QueryHandler, type IQueryHandler } from '@nestjs/cqrs';
 import { Inject } from '@nestjs/common';
 import { NotFoundException } from '@modules/shared/domain/domain-exception';
+import { CacheService, CachePrefix, CacheTTL } from '@modules/shared/infrastructure/cache.service';
 import { GetListingQuery } from './get-listing.query';
 import { LISTING_REPOSITORY, type IListingRepository } from '../../../domain/repositories/listing.repository';
 
@@ -59,13 +60,23 @@ export interface ListingDetailDto {
 export class GetListingHandler implements IQueryHandler<GetListingQuery> {
   constructor(
     @Inject(LISTING_REPOSITORY) private readonly listingRepo: IListingRepository,
+    private readonly cache: CacheService,
   ) {}
 
   async execute(query: GetListingQuery): Promise<ListingDetailDto> {
-    const result = await this.listingRepo.findByIdWithProperty(query.listingId);
-    if (!result) {
-      throw new NotFoundException('Listing', query.listingId);
-    }
-    return result as unknown as ListingDetailDto;
+    const cacheKey = CacheService.buildKey(CachePrefix.LISTING, query.listingId);
+
+    return this.cache.getOrSet(
+      cacheKey,
+      async () => {
+        const result = await this.listingRepo.findByIdWithProperty(query.listingId);
+        if (!result) {
+          throw new NotFoundException('Listing', query.listingId);
+        }
+        return result as unknown as ListingDetailDto;
+      },
+      CacheTTL.LISTING_DETAIL,
+      'listing',
+    );
   }
 }