11e1bbbab7
Previously the WeChat channel's send() method only handled text messages,
completely ignoring msg.media. When the agent called message(media=[...]),
the file was never delivered to the user.
Implement the full WeChat CDN upload protocol following the reference
@tencent-weixin/openclaw-weixin v1.0.2:
1. Generate a client-side AES-128 key (16 random bytes)
2. Call getuploadurl with file metadata + hex-encoded AES key
3. AES-128-ECB encrypt the file and POST to CDN with filekey param
4. Read x-encrypted-param from CDN response header as download param
5. Send message with the media item (image/video/file) referencing
the CDN upload
Also adds:
- _encrypt_aes_ecb() for AES-128-ECB encryption (reverse of existing
_decrypt_aes_ecb)
- Media type detection from file extension (image/video/file)
- Graceful error handling: failed media sends notify the user via text
without blocking subsequent text delivery
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>