White-label: title/logo now driven by conf (closes #6)

conf.name was already plumbed into routes/index.js's values object,
but never actually rendered anywhere -- <title>, the navbar brand,
and the favicon were all still hardcoded "SSO - Theta 42"/"SSO
Manager". Now render <%- name %>/<%- logo %> in top.ejs; new
conf.logo key (default: the existing theta42.svg) drives the navbar
image and favicon.

Also fixes a pre-existing broken favicon: top.ejs referenced
/static/favicon.svg, which was never actually served from public/ --
only public/img/theta42.svg existed. The favicon now uses that same
file via conf.logo instead of a nonexistent path.

Footer copyright/logo/GitHub links are left as-is (open-source
attribution, not deployment branding).

secrets.js.example

@@ -19,6 +19,7 @@
 module.exports = {
     port: 3001,
     name: 'SSO Manager',                 // shown in UI and outbound email
+    logo: '/static/img/theta42.svg',     // nav/favicon image; point at your own file under public/ to white-label
     ldap: {
         url: 'ldap://localhost',         // or ldaps://host:636 for TLS
         bindDN: 'cn=admin,dc=example,dc=com',