feat(platform): pass original image URL to Image component in 6 adapters (#2362)

Preserve the platform CDN URL in Image.url alongside base64 data,
enabling plugins to use ContentElement.from_image_url() for direct
vision API access without redundant local download.

- aiocqhttp: use msg_data["data"]["url"] and msg.data["url"]
- discord: use attachment.url
- telegram: use file.file_path
- slack: use pic_url
- wecom: use picurl
- qqofficial: use pic_url

Satori adapter already follows this pattern (satori.py:168).
The change is purely additive — base64 is preserved for backward
compatibility, and get_bytes() priority (url → base64 → path)
ensures plugins can choose the optimal path.

Closes #2355

Co-authored-by: douxt <8429023+douxt@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

src/langbot/pkg/platform/sources/aiocqhttp.py

@@ -240,7 +240,11 @@ class AiocqhttpMessageConverter(abstract_platform_adapter.AbstractMessageConvert
         async def process_message_data(msg_data, reply_list):
             if msg_data['type'] == 'image':
                 image_base64, image_format = await image.qq_image_url_to_base64(msg_data['data']['url'])
-                reply_list.append(platform_message.Image(base64=f'data:image/{image_format};base64,{image_base64}'))
+                reply_list.append(
+                    platform_message.Image(
+                        url=msg_data['data']['url'], base64=f'data:image/{image_format};base64,{image_base64}'
+                    )
+                )
 
             elif msg_data['type'] == 'text':
                 reply_list.append(platform_message.Plain(text=msg_data['data']['text']))
@@ -285,7 +289,9 @@ class AiocqhttpMessageConverter(abstract_platform_adapter.AbstractMessageConvert
                     image_msg = platform_message.Face(face_id=face_id, face_name=face_name)
                 else:
                     image_base64, image_format = await image.qq_image_url_to_base64(msg.data['url'])
-                    image_msg = platform_message.Image(base64=f'data:image/{image_format};base64,{image_base64}')
+                    image_msg = platform_message.Image(
+                        url=msg.data['url'], base64=f'data:image/{image_format};base64,{image_base64}'
+                    )
                 yiri_msg_list.append(image_msg)
             elif msg.type == 'forward':
                 # 暂时不太合理