fix: trust X-Forwarded-Proto header from Traefik proxy (#189)

Traefik terminates TLS and forwards requests over HTTP internally,
setting X-Forwarded-Proto: https. Without trusting this header,
Symfony generates http:// URLs (e.g. in password reset emails).

config/packages/framework.yaml

@@ -14,7 +14,7 @@ when@prod:
         # shortcut for private IP address ranges of your proxy
         trusted_proxies: 'private_ranges'
         # or, if your proxy instead uses the "Forwarded" header
-        trusted_headers: [ 'forwarded' ]
+        trusted_headers: [ 'x-forwarded-proto' ]
 
 when@test:
     framework: