Add end-to-end tests for TLS RPT report ingestion and WebSocket event handling

- Implemented tests for ingesting TLS RPT reports from emails and ensuring they are stored correctly in the database.
- Added tests to verify that the same report can be ingested multiple times without duplication.
- Created tests for backfilling reports that were previously delivered to the inbox.
- Developed WebSocket event handling tests to ensure events are correctly routed to subscribers based on mailbox ownership.
- Included tests for the mail API to validate session handling, mailbox isolation, and error mapping.
- Ensured that the API rejects unauthorized requests and handles malformed JSON gracefully.

migrations/0008_add_reports_folder.down.sql

@@ -0,0 +1,8 @@
+-- Only removes the folder where it is still empty. A Reports folder holding
+-- delivered reports is data, and dropping it would cascade those messages away.
+DELETE FROM folders f
+ WHERE LOWER(f.name) = 'reports'
+   AND f.special_use IS NULL
+   AND NOT EXISTS (
+     SELECT 1 FROM email_messages e WHERE e.folder_id = f.id
+   );