fix: add absolute_redirect off to prevent incorrect redirect URLs

nginx was converting relative redirects to absolute URLs using its internal
server context (http://...:8080) instead of preserving the original scheme
and host from the X-Forwarded headers. Adding absolute_redirect off ensures
browsers receive proper relative redirects that resolve correctly.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jensens

src/constructs/webmail-auth-proxy-configmap.ts

@@ -61,6 +61,10 @@ http {
         listen 8080;
         server_name _;
 
+        # Prevent nginx from converting relative redirects to absolute URLs
+        # This ensures redirects use the original scheme/host from X-Forwarded headers
+        absolute_redirect off;
+
         # Internal location for auth subrequest
         # Calls admin service's /internal/auth/user endpoint
         location = /_auth {