feat(ml): upload images to ML hosting + show earnings estimate on validate

- Add upload_image() to MeliService using ML /pictures endpoint
- Add get_listing_price() to fetch exact ML fees
- Auto-upload inventory images to ML before validate/publish
- Show fee breakdown and net earnings in validate modal
- Fallback to approximate fees (13-18%) if ML API fails

pos/services/meli_service.py

@@ -143,6 +143,66 @@ class MeliService:
             )
         return resp.json()
 
+    # ─── Images ──────────────────────────────────────────────────────────
+
+    def upload_image(self, image_path_or_url: str) -> dict:
+        """Upload an image to MercadoLibre's image hosting.
+
+        Accepts either a local file path or a URL.
+        Returns the ML picture dict with 'id' and 'secure_url' / 'url' keys.
+        """
+        import os
+        import requests as raw_requests
+
+        # If it's a URL, download it first
+        if image_path_or_url.startswith("http://") or image_path_or_url.startswith("https://"):
+            img_resp = raw_requests.get(image_path_or_url, timeout=30)
+            if not img_resp.ok:
+                raise MeliError(f"Failed to download image from {image_path_or_url}: {img_resp.status_code}")
+            file_bytes = img_resp.content
+            content_type = img_resp.headers.get("Content-Type", "image/jpeg")
+            filename = "image.jpg"
+        else:
+            if not os.path.exists(image_path_or_url):
+                raise MeliError(f"Image file not found: {image_path_or_url}")
+            with open(image_path_or_url, "rb") as f:
+                file_bytes = f.read()
+            content_type = "image/jpeg"
+            filename = os.path.basename(image_path_or_url)
+
+        upload_url = f"{BASE_URL}/pictures"
+        files = {"file": (filename, file_bytes, content_type)}
+        req_headers = {"Authorization": f"Bearer {self.access_token}"}
+        resp = raw_requests.post(upload_url, files=files, headers=req_headers, timeout=60)
+
+        if resp.status_code == 401 and self.refresh_token:
+            self._refresh_token()
+            req_headers["Authorization"] = f"Bearer {self.access_token}"
+            resp = raw_requests.post(upload_url, files=files, headers=req_headers, timeout=60)
+
+        if resp.status_code == 401:
+            raise MeliAuthError("Unauthorized. Token may be expired.", status_code=401, response_body=resp.text)
+        if not resp.ok:
+            raise MeliError(f"Image upload failed: {resp.status_code} {resp.text}", status_code=resp.status_code, response_body=resp.text)
+
+        return resp.json()
+
+    def get_listing_price(self, site_id: str, price: float, listing_type_id: str, category_id: str) -> dict:
+        """Get the exact fee / net amount for a given price, listing type and category.
+
+        ML endpoint: GET /sites/{site_id}/listing_prices
+        Returns dict with sale_fee_amount, net_amount, etc.
+        """
+        return self._request(
+            "GET",
+            f"/sites/{site_id}/listing_prices",
+            params={
+                "price": str(price),
+                "listing_type_id": listing_type_id,
+                "category_id": category_id,
+            },
+        )
+
     # ─── Items (listings) ────────────────────────────────────────────────
 
     def validate_item(self, payload: dict) -> dict: