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

internal/handlers/auth.go

@@ -1,7 +1,7 @@
 package handlers
 
 import (
-	"shelf/internal/database"
+	"bookmann/internal/database"
 	"fmt"
 	"net/http"
 	"time"