fix(bimi): as rotas existiam no protocols e o proxy nao as conhecia

O painel respondia "API endpoint not found" e o logotipo devolvia a pagina de
404 do Next. As rotas estavam registadas no servico protocols, mas o proxy do
webmail decide o upstream por uma lista propria, e eu nao acrescentei a "bimi"
-- exactamente o erro contra o qual o comentario dessa lista avisa.

Ficam ambas cobertas por testes: cada area administrativa que o protocols
possui, e o caminho well-known do logotipo. Esquecer isto nao volta a ser
silencioso.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

services/webmail/next.config.ts

@@ -30,6 +30,12 @@ const nextConfig: NextConfig = {
         source: "/.well-known/mta-sts.txt",
         destination: `${PROTOCOLS_SERVICE_URL}/.well-known/mta-sts.txt`,
       },
+      {
+        // Fetched by receiving mail providers evaluating a message, which
+        // hold no session and never will.
+        source: "/.well-known/bimi/default.svg",
+        destination: `${PROTOCOLS_SERVICE_URL}/.well-known/bimi/default.svg`,
+      },
       {
         source: "/.well-known/security.txt",
         destination: `${PROTOCOLS_SERVICE_URL}/.well-known/security.txt`,