Migrate to MyBatis with proper Controller→Service→Mapper layering

- Add MyBatis Spring Boot Starter with XML mappers and domain classes
- Create 9 mapper interfaces + XML: Restaurant, Video, Channel, Review,
  User, Stats, DaemonConfig, Search, Vector
- Create 10 domain classes with Lombok: Restaurant, VideoSummary,
  VideoDetail, VideoRestaurantLink, Channel, Review, UserInfo,
  DaemonConfig, SiteVisitStats, VectorSearchResult
- Create 7 new service classes: RestaurantService, VideoService,
  ChannelService, ReviewService, UserService, StatsService,
  DaemonConfigService
- Refactor all controllers to be thin (HTTP + auth only), delegating
  business logic to services
- Refactor SearchService, PipelineService, DaemonScheduler, AuthService,
  YouTubeService to use mappers/services instead of JDBC/repositories
- Add Jackson SNAKE_CASE property naming for consistent API responses
- Add ClobTypeHandler for Oracle CLOB→String in MyBatis
- Add IdGenerator utility for centralized UUID generation
- Delete old repository/ package (6 files), JdbcConfig, LowerCaseKeyAdvice
- VectorService retains JDBC for Oracle VECTOR type support

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

backend-java/src/main/resources/application.yml

@@ -29,6 +29,7 @@ spring:
 
   jackson:
     default-property-inclusion: non_null
+    property-naming-strategy: SNAKE_CASE
     serialization:
       write-dates-as-timestamps: false
 
@@ -57,7 +58,13 @@ app:
   cache:
     ttl-seconds: 600
 
+mybatis:
+  mapper-locations: classpath:mybatis/mapper/*.xml
+  config-location: classpath:mybatis/mybatis-config.xml
+  type-aliases-package: com.tasteby.domain
+  type-handlers-package: com.tasteby.config
+
 logging:
   level:
     com.tasteby: DEBUG
-    org.springframework.jdbc: DEBUG
+    com.tasteby.mapper: DEBUG