Add a real signup path instead of the accidental one

SAAS_PLAN.md 2.2: there was no /signup page. The only self-serve path was
Google sign-in on /login, which auto-provisions a Firebase account with no
role or org claim at all - previously that meant "viewer role, full read
access" the moment the AuthProvider cookie logic (previous commit) let it
through. That's closed now regardless; this commit is the other side of it
- giving people an actual way in.

app/signup/page.tsx: email/password (createUserWithEmailAndPassword) or
Google, same visual language as /login. It only creates the Firebase
account - org naming is deliberately not on this page, so every path that
produces an account with no org (this one, and Google-via-/login) converges
on the same next screen.

app/onboarding/page.tsx: that screen. Shown to any signed-in user with no
orgId (ChromeSwitcher's redirect, previous commit), collects an org name,
calls the new c2api.signup() -> POST /auth/signup (routers/links.py,
already shipped), then refreshClaims() to force-refetch the ID token so
orgId picks up immediately and the same redirect effect sends them on to
/dashboard - no manual reload needed.

lib/c2api.ts also gained getOrg/updateOrg and the enrollment-token
mint/list/revoke calls (routers/org.py, already shipped on the backend)
and joinWaitlist (routers/waitlist.py) - none consumed yet, wired in ahead
of the settings/legal commits that use them so this stays one add per
concept rather than scattering client additions across later commits.

/login gained a "Don't have an account? Sign up" link to /signup. This is
signup plumbing, not marketing copy - pricing/plan copy (app/pricing,
lib/billing.ts) is untouched in this pass, that's a separate, still-open
decision (SAAS_PLAN.md section 6).

Typecheck: clean (tsc --noEmit via the WSL-native ~/drb-frontend copy).

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

drb-frontend/app/login/page.tsx

@@ -105,6 +105,11 @@ export default function LoginPage() {
           </svg>
           Continue with Google
         </button>
+
+        <p className="text-center text-xs text-gray-500">
+          Don&apos;t have an account?{" "}
+          <Link href="/signup" className="text-indigo-400 hover:text-indigo-300 transition-colors">Sign up</Link>
+        </p>
       </div>
     </div>
   );