Attachment webhook event payloads (`message_created`) were missing the
file extension and content type. The `extension` column existed but was
never populated, and `content_type` was not included in the payload at
all.
## What changed
- Added `before_save :set_extension` callback to extract file extension
from the filename when saving an attachment.
- Added `content_type` (from ActiveStorage) to the `file_metadata` used
in `push_event_data`.
### Before
```json
{
"extension": null,
"data_url": "...",
"file_size": 11960
}
```
### After
```json
{
"extension": "pdf",
"content_type": "application/pdf",
"data_url": "...",
"file_size": 11960
}
```
## How to reproduce
1. Send a message with a file attachment (e.g., PDF) via any channel
2. Inspect the `message_created` webhook payload
3. Observe `extension` is `null` and `content_type` is missing
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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