feat(caddy): support HTTPS upstreams via https:// prefix

When a route's upstream starts with https://, buildCaddyfile emits a
transport http { tls_insecure_skip_verify } block so Caddy connects over TLS
and accepts the self-signed certificate typical of backends like Semaphore.
Added a UI hint explaining the https:// prefix.

src/components/Settings.tsx

@@ -930,6 +930,7 @@ export default function Settings({ currentUser: _currentUser }: SettingsProps) {
           {caddyEnabled && (
             <div className="space-y-2">
               <Label>Proxy Routes</Label>
+              <Hint>Prefix the upstream with https:// for TLS backends (e.g. Semaphore) — the certificate is not verified.</Hint>
 
               {caddyStatus === 'unavailable' && (
                 <p className="text-[11px] font-mono text-amber-400 mb-2">