Remove item ID column references - items now use composite PK (guid, feed_url)

- Remove ID field from Item struct
- Remove ID field from SearchItem struct
- Update all SQL queries to not select id column
- Change MarkItemPublished to use feedURL/guid instead of id
- Update shortener to use item_guid instead of item_id
- Add migration to convert item_id to item_guid in short_urls table
- Update API endpoints to use feedUrl/guid instead of itemId

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -11,9 +11,9 @@ services:
     environment:
       DB_HOST: infra-postgres
       DB_PORT: 5432
-      DB_USER: news_1440
+      DB_USER: dba_1440_news
       DB_PASSWORD_FILE: /run/secrets/db_password
-      DB_NAME: news_1440
+      DB_NAME: db_1440_news
     secrets:
       - db_password
     volumes:
@@ -55,7 +55,7 @@ services:
 
 secrets:
   db_password:
-    file: ../../../infra/postgres/secrets/news_1440_password.txt
+    file: ../../../infra/postgres/secrets/dba_1440_news_password.txt
 
 networks:
   proxy: