Bug Fix: Slack Notification Not Sent When Ticket Marked as "Done" in Notion

[aliyamuqaddas]

Summary

This PR fixes an issue where marking a ticket as "Done" in Notion did not trigger the expected Slack notification. The problem was due to silent failures and missing validations in the Slack notification flow.

✅ Fixes

• post_message/2 in JumpTickets.External.Slack was returning nil for an empty channel ID, causing silent failures.
• No validation existed to check whether a valid Slack channel ID was extracted from the channel URL.
• The DoneNotifier module lacked proper error handling and logging, making the issue hard to trace.
• TicketDoneController did not report specific error reasons.

🔧 Changes Made

• Improved post_message/2:
  Returns {:error, :empty_channel_id} if the channel ID is empty.

• Validated Slack channel ID:
  Ensures the channel ID is non-empty before sending messages.

• Improved error handling in notify_ticket_done/3:
  Now matches and logs specific error cases (e.g., empty channel ID, invalid URL).

• Enhanced logging and error responses in controller:
  Clearer error messages make debugging easier and improve reliability.

🧪 Testing

Manually verified the following scenarios:

• ✅ Valid Slack channel URL → notification sent

• ❌ Empty channel ID → returns {:error, :empty_channel_id}
• ❌ Invalid Slack channel URL format → handled gracefully
• ❌ No Slack channel provided → descriptive error logged