feat: Improve file display, timezone handling, and LOT management

Changes:
- Fix datetime serialization with UTC 'Z' suffix for correct timezone display
- Add PDF upload support with extension fallback for MIME detection
- Fix LOT add/remove by creating new list for SQLAlchemy JSON change detection
- Add file message components (FileMessage, ImageLightbox, UploadPreview)
- Add multi-file upload support with progress tracking
- Link uploaded files to chat messages via message_id
- Include file attachments in AI report generation
- Update specs for file-storage, realtime-messaging, and ai-report-generation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/modules/chat_room/services/room_service.py

@@ -467,7 +467,11 @@ class RoomService:
                             f"Failed to delete report file: {report.docx_storage_path}"
                         )
 
-            # Step 3: Delete room from database (CASCADE handles related tables)
+            # Step 3: Delete reports from database (before room delete due to relationship handling)
+            for report in reports:
+                db.delete(report)
+
+            # Step 4: Delete room from database (CASCADE handles other related tables)
             db.delete(room)
             db.commit()