feat: let existing users log in while new sign-ups are paused

Re-enable the GitHub login button with an 'Already have access?' framing and a
note that new sign-ups are paused. New-user creation stays blocked server-side
(databaseHooks.user.create.before), so only existing users get in.

Author: ripgrim

apps/web/src/components/layout/auth/login-page.tsx

@@ -1,3 +1,4 @@
+import { useQuery } from "@tanstack/react-query"
 import { useNavigate } from "@tanstack/react-router"
 import { authClient } from "@tripwire/auth/client"
 import { useEffect } from "react"
@@ -16,6 +17,19 @@ export function LoginPage() {
   const navigate = useNavigate()
   const { data: session, isPending } = authClient.useSession()
 
+  const { data: loginUrl } = useQuery({
+    queryKey: ["github-login-url"],
+    enabled: !isPending && !session,
+    queryFn: async () => {
+      const { data } = await authClient.signIn.social({
+        provider: "github",
+        callbackURL: "/rules",
+        disableRedirect: true,
+      })
+      return data?.url ?? null
+    },
+  })
+
   useEffect(() => {
     if (!isPending && session) {
       navigate({ to: "/" })
@@ -29,18 +43,21 @@ export function LoginPage() {
   return (
     <div className="flex h-screen w-full shrink-0 flex-col items-center justify-center gap-8 bg-[#191919] px-6 antialiased [font-synthesis:none]">
       <TripwireLogo className="h-10 w-10 text-white" />
-      <div className="flex flex-col items-center gap-4">
+      <div className="flex flex-col items-center gap-3">
+        <span className="text-[14px] text-tw-text-secondary">
+          Already have access?
+        </span>
         <Button
-          disabled
+          render={<a href={loginUrl ?? undefined} />}
+          loading={!loginUrl}
           variant="outline"
           size="sm"
-          className="border-[#CDCDCD] bg-white text-black opacity-60"
+          className="border-[#CDCDCD] bg-white text-black hover:bg-white/90"
         >
           Log in
         </Button>
-        <p className="max-w-xs text-center text-[13px] leading-relaxed text-tw-text-secondary">
-          Sign-ups are paused for now — we're keeping things small while we
-          rework a few things under the hood. Check back soon.
+        <p className="max-w-xs text-center text-[12px] leading-relaxed text-tw-text-muted">
+          New sign-ups are paused for now — check back soon.
         </p>
       </div>
     </div>