fix: compressão real p/ stream DCTDecode + auth c/ chave vazia

- Substitui xobj._data por page.images[].replace() em compress.py e pdfa.py
- Adiciona compress_with_stats() com feedback honesto na UI
- Trata PDFTOOLKIT_API_KEY vazia como modo dev (auth desabilitado)
- Atualiza engine.py e app.py para exibir redução real ou 'já otimizado'

core/pdfa.py

@@ -139,30 +139,36 @@ def strip_pdfa(data: bytes) -> bytes:
 def compress_pdfa(data: bytes, quality: int = 60, max_dim: int = 2000) -> bytes:
     """
     Comprime imagens internas mantendo a estrutura PDF/A.
-    Usa a mesma lógica de compress.compress_pdf mas preserva
-    metadados XMP e OutputIntents.
+    Usa a mesma lógica de compress_pdf (ImageFile.replace)
+    mas preserva metadados XMP e OutputIntents.
     """
-    from .compress import _downsample_image
+    from PIL import Image as PILImage
+    from .compress import _prepare_image
 
     reader = PdfReader(io.BytesIO(data))
-    writer = PdfWriter()
-    writer.metadata = reader.metadata
+    writer = PdfWriter(clone_from=reader)
 
-    for page in reader.pages:
-        if "/XObject" in page.get("/Resources", {}):
-            xobjects = page["/Resources"]["/XObject"]
-            for obj_name in list(xobjects.keys()):
-                xobj = xobjects[obj_name]
-                if xobj.get("/Subtype") == "/Image":
-                    try:
-                        raw = xobj.get_data()
-                        if raw:
-                            compressed = _downsample_image(raw, quality, max_dim)
-                            xobj._data = compressed
-                    except Exception:
-                        pass
-        writer.add_page(page)
+    replaced = 0
+    for page in writer.pages:
+        try:
+            images = list(page.images)
+        except Exception:
+            continue
+        for img_file in images:
+            if getattr(img_file, "indirect_reference", None) is None:
+                continue
+            try:
+                pil = img_file.image
+                if pil is None:
+                    continue
+                prepared, save_kwargs = _prepare_image(
+                    pil, quality=quality, max_dim=max_dim
+                )
+                img_file.replace(prepared, **save_kwargs)
+                replaced += 1
+            except Exception:
+                pass
 
     out_buf = io.BytesIO()
-    writer.write_stream(out_buf)
+    writer.write(out_buf)
     return out_buf.getvalue()