nixos-module: fix caddy Host-header matching for 127.0.0.1/[::1]

Caddy strictly matches vhosts on the exact Host header, unlike nginx
where a single vhost acts as the default regardless of Host. With
hostname = "localhost" (the local-dev default), visiting the VM via
http://127.0.0.1:PORT instead of http://localhost:PORT sent a Host
header matching no vhost, and Caddy silently returned an empty 200 OK
- a genuine white screen with no error anywhere (not in the console,
not in the network tab).

Adds serverAliases for 127.0.0.1:80 and [::1]:80 to the caddy vhost
when hostname is "localhost", so all three ways of reaching the local
VM resolve to the same site block. Verified directly: before this
fix, curl with `Host: 127.0.0.1` got an empty response while `Host:
localhost` got the full app shell; after, all three (localhost,
127.0.0.1, [::1]) return the same 200 response.

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

nixos-module/invoiceninja.nix

@@ -557,6 +557,14 @@ in
           cfg.proxy.caddyConfig
           {
             hostName = lib.mkForce proto_hostname;
+            # Caddy matches vhosts on the exact Host header, unlike nginx's single-vhost-is-default
+            # behavior. For local dev, accept requests to 127.0.0.1/[::1] too - otherwise visiting
+            # via the IP literal instead of "localhost" hits no vhost and gets an empty 200 response
+            # (a silent white screen, no error anywhere).
+            serverAliases = lib.mkIf (cfg.hostname == "localhost") [
+              "127.0.0.1:80"
+              "[::1]:80"
+            ];
             extraConfig = ''
               encode zstd gzip
               root ${invoiceninja}/public