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/wecom.py

@@ -133,7 +133,9 @@ class WecomMessageConverter(abstract_platform_adapter.AbstractMessageConverter):
         yiri_msg_list = []
         yiri_msg_list.append(platform_message.Source(id=message_id, time=datetime.datetime.now()))
         image_base64, image_format = await image.get_wecom_image_base64(pic_url=picurl)
-        yiri_msg_list.append(platform_message.Image(base64=f'data:image/{image_format};base64,{image_base64}'))
+        yiri_msg_list.append(
+            platform_message.Image(url=picurl, base64=f'data:image/{image_format};base64,{image_base64}')
+        )
         chain = platform_message.MessageChain(yiri_msg_list)
 
         return chain