refactor: move backend files to backend/ directory

Reorganize project structure:
- backend/cmd/openteam/ — entry point
- backend/internal/ — core packages
- backend/middleware/ — HTTP middleware
- backend/router/ — route setup
- backend/wire/ — dependency injection
- backend/pkg/ — shared utilities
- backend/go.mod, go.sum — Go module files

Updated Makefile to work from backend/ directory.
Removed old lowercase makefile.

backend/internal/utils/convert.go

@@ -0,0 +1,16 @@
+package utils
+
+import "strings"
+
+func StringToBool(strSlice []string) []bool {
+	boolSlice := make([]bool, len(strSlice))
+	for i, str := range strSlice {
+		str = strings.ToLower(str)
+		if str == "true" {
+			boolSlice[i] = true
+		} else if str == "false" {
+			boolSlice[i] = false
+		}
+	}
+	return boolSlice
+}