refactor: rename project back from shelf to bookmann

- Change Go module name back from 'shelf' to 'bookmann'
- Update all import paths back to 'bookmann' module
- Update README.md project name back to 'Bookmann'
- Update docker-compose.yml container names back to 'bookmann' and 'bookmann_db'
- Regenerate database code with restored module imports

docker-compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 services:
   db:
     image: postgres:15-alpine
-    container_name: shelf_db
+    container_name: bookmann_db
     environment:
       POSTGRES_DB: ebookdb
       POSTGRES_USER: postgres
@@ -25,7 +25,7 @@ services:
     build:
       context: .
       dockerfile: ./Dockerfile
-    container_name: shelf
+    container_name: bookmann
     environment:
       DATABASE_HOST: db
       DATABASE_PORT: 5432