refactor(backend): layout canonique cmd/server + models/service/ocr/pkg + fix compilation héritée

backend/ocr/engine.go

@@ -0,0 +1,10 @@
+package ocr
+
+import "context"
+
+// Engine extracts text from a document (image or PDF) located at filePath.
+// The V1 implementation is a Tesseract system call (OCR_LANG, défaut fra+eng);
+// swapping to a remote service later only changes the injection point.
+type Engine interface {
+	ExtractText(ctx context.Context, filePath string, lang string) (string, error)
+}