Add screenshot uploads to feedback modal, Webex bot DM on issue close

- Feedback modal now supports up to 3 image attachments (PNG/JPG/GIF/WebP, 5MB
  each) with thumbnail previews. Images are uploaded to GitLab project uploads
  and embedded as markdown in the issue description.
- New webhook endpoint (POST /api/webhooks/gitlab) receives issue close events,
  parses the submitter from the description, looks up their email, and sends a
  Webex DM via the Patches O'Houlihan bot.
- New helper: backend/helpers/webexBot.js (fire-and-forget DM sender).
- Requires WEBEX_BOT_TOKEN and GITLAB_WEBHOOK_SECRET in backend/.env.

backend/server.js

@@ -33,6 +33,7 @@ const createAtlasRouter               = require('./routes/atlas');
 const createJiraTicketsRouter         = require('./routes/jiraTickets');
 const createCardApiRouter             = require('./routes/cardApi');
 const createFeedbackRouter            = require('./routes/feedback');
+const createWebhooksRouter            = require('./routes/webhooks');
 
 const app = express();
 const PORT = process.env.PORT || 3001;
@@ -230,6 +231,9 @@ app.use('/api/card', createCardApiRouter());
 // Feedback routes — bug reports and feature requests to GitLab
 app.use('/api/feedback', createFeedbackRouter());
 
+// GitLab webhook routes — receives issue lifecycle events (no auth required)
+app.use('/api/webhooks', createWebhooksRouter());
+
 // ========== CVE ENDPOINTS ==========
 
 // Get all CVEs with optional filters (authenticated users)